drm/komeda: Add event handling for EMPTY/FULL

EMPTY/FULL are HW input/output FIFO condition identifer, which are
useful information for addressing the problem, so expose them.

Signed-off-by: james qian wang (Arm Technology China) <james.qian.wang@arm.com>
Reviewed-by: Mihail Atanassov <mihail.atanassov@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191212072737.30116-1-james.qian.wang@arm.com