SAMV7: Add framework for USB DCD.  Initial check-in is just the SAMA5 USB DCD with naming changes to get a clean compilation.  Needs careful review and comparison with datasheet and, of course, testing

Update some recent Tiva changes so that old LM3S parts at least still build (but have not been retested)

instead of Kconfig to help reduce bloat and confusion.
- Timer changed to remove ADC coupling in Kconfig to code and moved
configuration up from arch/arm/src/tiva to configs/tm4c123g-launchpad/src.
- GPIO driver needed small fixes in the configuration routines and
discovered false-positive bugs in interrupt testing: interrupts are now
verified to actually be working reliably.
- Attempt to apply some consistency in the tiva arch/ level's interface
to the config/board/ level driver configuration.

From Calvin Maguranis