drm/amd/display: Fix deadlock when flushing irq

Lock irq table when reading a work in queue,
unlock to flush the work, lock again till all tasks
are cleared

Signed-off-by: Mikita Lipski <mikita.lipski@amd.com>
Reviewed-by: Harry Wentland <Harry.Wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>