examples/touchscreen:  Add a configuration option to indicate that there is or is not an architecture-specific initialization function

SAMA5: The PIO used for the red LED is also used as the camera module reset line:  Added a configuration option to suppress use of the red LED if the PIO is used for another purpose.  Reported by David Sidrane.

configs/*/defconfig: Increase the number of pre-allocated watchdogs in configurations that use networking or USB

SAMA5: On some hardware, reconfiguring the PLL while executing out of NOR FLASH causes crashes.  This was fixed by David Sidrane by implementing RAM functions. The killer code is copied and executed from ISRAM and the crash is avoided.

If LOWVECTORS is selected, then we need to clear the VBAR register.  A bootloader may have left the VBAR in an bad state

SAMA5D3x-EK: Change name of all board-specific configuration variables so that there are no collisions with names of similar variables for other boards