arch/arm/src/tiva: Fix compilation errors on Tiva ADC code when ADC is enable.  Please several cosmetic changes to files made during code review.

Provide a user defined callback context for irq's, such that when
registering a callback users can provide a pointer that will get
passed back when the isr is called.

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

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