Revert "drm/radeon: disable CIK CP semaphores for now"

This reverts commit 99b4f251.

Semaphores work fine after further review and testing.
Cc: 3.13 <stable@vger.kernel.org> # 3.13

drivers/gpu/drm/radeon/cik.c

@@ -3566,8 +3566,6 @@ bool cik_semaphore_ring_emit(struct radeon_device *rdev,
 			     struct radeon_semaphore *semaphore,
 			     bool emit_wait)
 {
-/* TODO: figure out why semaphore cause lockups */
-#if 0
 	uint64_t addr = semaphore->gpu_addr;
 	unsigned sel = emit_wait ? PACKET3_SEM_SEL_WAIT : PACKET3_SEM_SEL_SIGNAL;
 
@@ -3576,9 +3574,6 @@ bool cik_semaphore_ring_emit(struct radeon_device *rdev,
 	radeon_ring_write(ring, (upper_32_bits(addr) & 0xffff) | sel);
 
 	return true;
-#else
-	return false;
-#endif
 }
 
 /**