kinetis: Fix bin file generation regression

Changes in ARMmbed#959 created an issue for GCC builds of k26f_bl, kl26z_bl, and k20dx_bl
in the generation of .bin file:

```
../../../tools/post_build_script_gcc.py
build/k26f_bl_crc
Error - only 1 region allowed in hex file 2 found.
Regions:
 0: 0x00000000 - 0x000003bf
 1: 0x00000400 - 0x0000ffff
```

Update hook to skip blinking on WebUSB HID serial traffic.

Move usbd_hid_no_activity() hook from usbd_user_hid.c to
DAP_queue.c and rename it to DAP_activity_blink().

In this new location it can be used to skip HID LED blinking in
traffic from USB bulk as well.

Add default behaviour of skipping HID blink of DAP serial & MSD
activity to the default hook for all projects.

Remove customised hooks in the artemis & micro:bit projects as they
are no longer needed.

microbitv2: Don't calculate the power source in the USB insertion int…

…errupt.

As it caused problems in the KL27 port with a timer interrupt being
set up to wait for 3 ms inside the USB insertion interrupt.

Sets the timer interrupt to level 2 (second lowest, but higher
than the wake up pin and USB insertion), as the default is
level 0, over other important interrupts like USB and I2C.

Also removes the need to check for the power source when the
Interface is requested to go to sleep, as it only really needs to
know if it's "USB connected" (being on battery or USB power bank
should have the same effect, it should not behave differently in
battery power vs USB power bank).

tools: Python 3 updates for combine_images.py.

Merge develop into main (ARMmbed#880)

In anticipation of v0257 release

nrf52820_microbit: Reduce CDC buffer size to 64B to reduce WebUSB los…

…t chars.

Issue discussion: ARMmbed#903

nrf52820_hic: Update board IDs used.

Correct UART pins on the nrf528xx

Flip TX and RX so the UART is setup correctly.

Fix dropped uart TX data on nRF52840

If uart data is being transmitted and uart_write_data is called
it will start a new transfer and clobber the currently transmitting
data.

This patch prevents that by only starting a transfer if there is not
one occurring already. Additionally to prevent race conditions between
interrupt and non-interrupt code, this patch only starts TX from the
uart interrupt handler.

ARMmbed#99 Enable flash protection on DAPLink bootloader region

- Set backdoor key to 'MICROBIT'.
- Enable FPROT for first 32 kB of flash.
- Fix FPROTx numbering according to KL27 RM, where FPROT3 is at address 0x408.
- Enable backdoor key in FSEC.
- Added asterisks next to selected options in comments for FOPT and FSEC.