Extract core USB serial functionality in a new usb_serial_port C class,
to allow creating multiple USB serial instances without duplicating all
code.

The original API is retained by creating static inline functions and
preprocessor macros using the old names, which are wrappers around the
new usb_serial_port functions and data members.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

Create a macro to emit all values for a CDC Interface Association
Descriptor, and use it.

This will avoid duplication when adding support for multiple USB serial
interfaces.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

Create a macro to emit all values for the various CDC descriptors, and
use it.  Note that this does not include the CDC Interface Association
Descriptor, as the latter is needed only for composite USB devices.

This will avoid duplication when adding support for multiple USB serial
interfaces.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

Include <usb_serial.h> instead of duplicating the needed forward
declarations.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

When including "core_pins.h":

    teensy3/usb_dev.c: In function '_reboot_Teensyduino_':
    teensy3/usb_dev.c:899:1: warning: 'noreturn' function does return

Fix this by adding a call to __builtin_unreachable().

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

- usb_serial_class::readBytes() calls millis(), hence it should
    include "core_pins.h",
  - usb_serial_flush_callback() is a public function, but is not
    declared in the header file.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

When processing CDC_SET_CONTROL_LINE_STATE and CDC_SET_LINE_CODING
requests, wIndex is ignored.  Hence if the CDC Status Interface is
enabled, these requests are always processed, even when not destined for
the actual serial status interface.

Fix this by adding a check to ensure that wIndex matches the CDC status
interface.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

fix panic-temp power off

The fix of IOMUXC_GPR_GPR16 disabled the power-off on panic-alarm, this should fix it.

T4 - USB Keyboard support LEDS

USB Flightsim for Teensy 4, add FlightSimData and FlightSimEvent data types for T3

Needs accompanying changes in Arduino's boards.txt, enabling corresponding menu entries

Sorry pasted in wrong code.

Migrated the T3 code over to handle the message to set the logical keyboard LEDS

As per forum thread: https://forum.pjrc.com/threads/59372-Teensy-4-0-no-support-for-keyboard_leds

SCB_ID_CSSELR is not const

T4 IntervalTimer - change limit magic number

Longer term we might consider changing timer over to using system clock, with default(max) divisior of 4 to go to PID instead of fixed 24mhz...

But in the mean time, try to allow IntervalTimer Settings that work at least as well as default settings for T3.2 whoes BUS speed is 48mhz, so the magic number of 36 was used which allowed a minimum value passed into begin/update of 36
48*.75-.5

With T4 code we just blindly left the magic number of 36...  So this one simply sort of halves it.  24*.75-.5 ... I rounded down to 17

fixes #418

fixes #293, fixes #414

T4 IntervalTimer Priority

If you call set priority it was only looking at priority of first two items, even though there could be 4.  The main code that started an interrupt checked all 4. So I sort of copied that code over, only change was to simply set the top_priority to the first item to start with instead of 255 and then look at the first item

Update imxrt.h

Add T4 ADC_ETC definitions for bits plus structure

Decided to go to the format that is closer to the the manual to
and use names like: chain_1_0, chain_3_2...

https://forum.pjrc.com/threads/58667-Temboo-library-error-Unknown-type-name-bool

T4 - Can now handle sketches with main() instead of setup()/loop()