drm/mediatek: Use spin_lock_irqsave() for CRTC event lock

Use the state-aware spin_lock_irqsave() and spin_unlock_irqrestore()
to avoid unconditionally re-enabling the local interrupts.

Fixes: 411f5c1e ("drm/mediatek: handle events when enabling/disabling crtc")
Signed-off-by: Fei Shao <fshao@chromium.org>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20240828101511.3269822-1-fshao@chromium.org/


Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>