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

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.

Teensy3 usb triple serial

shiftout: highest speed 10MHz