Implement a blinking LED using Timer Counter 0

Sadly the LED is connected to a GPIO doesn't have useful functions.
The only other function is ETM tracing.
The GPIO can't be controlled by a Timer Counter (TC) or
Timer Counter for Control (TCC) because only certain GPIOs
are able to be controlled by it.

Use a Timer Counter to count the time in one-shot mode
and trigger the LED from the main main loop.
This has the advantage of keeping the interference to a minimum in difference
to a Timer Counter interrupt.
Additional by using the ARM core to change the LED, it can be used as heart beat,
if the LED blinks, the ARM core is still 'alive'.

There are other possibilities to trigger the LED:
- use a TC to trigger the Event System, which toggles the GPIO.
- use a TC to trigger the DMA engine, which transfer 1 byte toggles the GPIO.

Change-Id: I8144120d07f73356855d084016edcb77d202da7f
---
M driver_init.c
M driver_init.h
M gcc/Makefile
A timer.c
A timer.h
M usb_start.c
6 files changed, 108 insertions(+), 3 deletions(-)