Changeset 1258229 in rtems for c/src/lib/libbsp/arm/raspberrypi

arm/raspberrypi: add locking around GPIO pin function selection.

This is required if function or direction is changed by some driver
after start of thread multitasking or in interrupts drivers.

There can be problem with calling GPIO function selection before
data section is initialized. But actual ticket lock implementation
seems to be compatible even with memory initialized to zero oven
on SMP.