unified: Add support for semaphore groups

Semaphore groups are enabled by default. Disabling them will both
decrease the footprint as well as improve the performance of the
k_sem_give() routine.

Change-Id: If6c1b0e2e1f71afd43e620f05f17068039d12b05
Signed-off-by: Peter Mitsis <peter.mitsis@windriver.com>