drm/msm/mdp5: Use the new hierarchy and drop old irq management

Call msm_mdss_init in msm_drv to set up top level registers/irq line.
Start using the new kms_init2/destroy2 funcs to inititalize MDP5 KMS.

With the MDSS interrupt and irqdomain set up, the old MDP5 irq code
can be dropped.

The mdp5_hw_init kms func now uses the platform device tied to MDP5
instead of the one tied to the drm_device/MDSS.

Signed-off-by: Archit Taneja <architt@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>