Upstream_nucleo 144

libc/hex2bin:  Move the portable library portion of apps/system/hex2bin to nuttx/libc/hex2bin where it can be shared with the OS internals.

 are held in the microcontrollers memory and only written to the IO-Expander.
 This reduces bus traffic and is more error-proof than the normal read-
 modify-write operation.

 Retry Mode: If enabled and an error occurs while writing to the IO-Expander the
 current transmission is automatically repeated once.

Add support for the Olimex STM32 E407

usb

Backout most of changes from 4d331ec09b2fc72636f86be628ea2f69381 and 8afe7216.  Does not work as expected.

Upstream_nucleo 144

 - sam_gpioread: Now the actual line level from the pin is read back.  This is extremely important for Open-Drain Pins, which can be used bidirectionally
 - Re-Implemented twi_reset-function and enhanced it so it can be called from inside the driver (see next point)
 - Glitch-Filter: Added a configuration option to enable the twi-built-in glitch filter
 - Added a "Single Master Mode": In EMC Testing the TWI-Bus got stuck because the TWI-Master detected a Multi-Master access (but there is no second master). With the option "Single Master" we detect these events and automatically trigger a twi_reset. We also do an automatic recovery if a slave got stuck (SDA stays low).

With the above changes I²C-Bus reliability in harsh environments (eg. EMC) is greatly improved.

The small change in the GPIO-Driver was necessary because otherwise you cannot read back the correct line status of Open-Drain Outputs and this is needed by the twi_reset function.

drivrs/ioexpander:  Add support for a very simple GPIO drivers.  It supports only pre-conrigured input and output pins and only basic input and output operations.

Add configuration logic to include a Kconfig file in each custom configuration.  Includes adding a dummy custom board configuration directory.  A consequence of this that each custom board directory will now need to contain a Kconfig file.  NOTE also that the new board directory does not take effect in the configuration menues until the NEXT time you run 'make menuconfig'

Stm32can: Port STM32L4 work to STM32