Initial commit. Compile checked only.

The High Gain bit in MCG_C1 was preventing teensy from booting
except after a programming session. The second change doesn't appear
to change any functionality, but complies with restrictions in the k20
family reference manual on FEI -> FBE clock transiions.

assert: Check if NDEBUG is defined

Refactored configs/nucleo-144 sub-directories to support additional nucleo-144 board.  Add support for the Nucleo-F767ZI board.

Add stm32f105r support

Kinetis usb driver

First attempt at a usb device controller driver for kinetis. derived from pic32mx usb driver, which uses the same usb controller.

STM32: Fix typo

Just update duty if frequency is not changed and PSM started.  This removeis glitch or blinking when only duty is frequently changed.