RX with 4 transfers using similar code to seremu

usb.c / interrupt - callbacks use ctz()

fix descriptor for teensy 4 usb audio midi serial

https://forum.pjrc.com/threads/60174-Understanding-The-USB-Specification

Fix Macro clockCyclesPerMicrosecond

The actual objects were not created like they were on the T3.x side, so just copied it over from there.

usb.c did not include the usb_rawhid.h so it would give a compiler warning about having to create a ...

Decided to go ahead and move the TX Buffer there as well
Did a quick check in earlier test program to echo the contents back.

The other test program was already setup to receive data on the HID and does hex dump of buffer which looks correct.  So far so good.

Testing against issues of hang from thread:
https://forum.pjrc.com/threads/59881-RawHID-recv()-hangs-after-updating-to-Teensyduino-1-4-9-or-higher-for-Teensy-4-0/page2

F_CPU -> F_CPU_ACTUAL

Fix comment re: systick

fix EWM address

#define FLASHMEM

be compatible with teensy 4

update macro analogInputToDigitalPin

This answers a long standing question :-)

https://github.com/PaulStoffregen/cores/issues/424#issue-555760117

see RM V2 Page 3221

https://forum.pjrc.com/threads/59815-teensy-4-0-XBAR-questions?p=231803&viewfull=1#post231803

Added Contact Count to Teensy3 multi touch report

https://forum.pjrc.com/threads/59815-teensy-4-0-XBAR-questions

teensy3: usb_serial: Fix port 2/3 mismatch

The code for the second port was accidentally expanded into
usb_serial3.c, while the code for the third port was expanded in
usb_serial2.c.

Fixes: cd4c30fde5 ("Expand all USB serial 2 & 3 stuff (needed for Arduino IDE use)")
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

This reverts commit dc46850b68.

This reverts commit a0ea852ed0.

This reverts commit 6fb4c61b45.

This reverts commit 68b0b84c58.