drm/msm/dpu: use kms stored hw mdp block

Avoid querying RM for hw mdp block. Use the one
stored in KMS during initialization.

changes in v4:
	- none
changes in v5:
	- none

Signed-off-by: Jeykumar Sankaran <jsanka@codeaurora.org>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>