undocumented SNVS regs

use GPIO6..9

add SNVS definitions for RTC

add #define digitalPinToInterrupt(p)

todo:
analogInputToDigitalPin(p)
digitalPinHasPWM(p)

Add SD Cards as IO pins - plus fix Serial2 and Serial8 for T4 B2

Fixed the Serial2 object to use the new correct pins, plus made Serial8 only valid for T4 B1 (not B2).

Also I defined IO pins for the six signals associated with the SD Card slot.

I have tested these both as IO pins and now as SPI2

update setpad in Analog.c and added debug info in startup

Fix SPDF Base-Address

Startup: save RAM with .progmem

T4 Imxrt define Flexio structure.

Moved from my flexio_t4 library.
Libary was updated to see if already defined before it now defines it.

clock halved - halve blink wait count

more defs

For review - Expose alt weak func(), label displayed dump

pendablesrvreq_isr = priority 32;

add some definitions for audio

speed optimize intervalTimer

Code from :: https://community.nxp.com/thread/389002
Name the fault dump info
New weak to override :: HardFault_HandlerC()

T4 - setTX with open drain mode.