Fix compilation errors in debug mode of stm32_pwm.c

Networking:  In both IPv6 and IPv4 incoming logic:  (1) Should check if the packet size is large enough before trying to access the packet length in the IP header.  (2) In the comparison between the IP length and the full packet length, need to subtract the size of the link layer header before making the comparison or we will get false positives (i.e., the packet is really too small).

Teensy clock fixes.

Added driver of IS25xP SPI flash devices

All configurations that have both CONFIG_NSH_LIBRARY=y and CONFIG_NET=y must now also have CONFIG_NSH_NETINIT=y

Refresh all configurations that have both CONFIG_NSH_LIBRARY and CONFIG_NET set in preparation for another change.

Fix STM32 DMA code and configuration for STM32F37X chips

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.

Based on sst25xx driver

Signed-off-by: Marten Svanfeldt <marten@intuitiveaerial.com>

Signed-off-by: Marten Svanfeldt <marten@intuitiveaerial.com>

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