drm/msm/sde: update irq enable/disable APIs

Update irq enable/disable APIs to use nolock version, and replace
atomic_dec_return with atomic_add_unless to prevent irq enable_count
from decreasing to negative number.

Change-Id: I57bfe381b102fcbaa5b6b9ab38dc71f1294a9b19
Signed-off-by: Ping Li <pingli@codeaurora.org>