drm/msm/dpu: allow initialization of encoder locks during encoder init

[ Upstream commit 2e7ec6b5297157efabb50e5f82adc628cf90296c ]

In the current implementation, mutex initialization
for encoder mutex locks are done during encoder
setup. This can lead to scenarios where the lock
is used before it is initialized. Move mutex_init
to dpu_encoder_init to avoid this.

Signed-off-by: Krishna Manikandan <mkrishn@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>