drm/msm/dpu: iterate for assigned hw ctl in virtual encoder

In virtual encoder modeset, DPU makes RM request to assign hw blocks
for the display. It is also expected in modeset to iterate and
associate the physical encoders with their relevant hw blocks.
Ping pong blocks are already handled here but hw ctl blocks are not.
This change moves the hw_ctl iteration and mapping from physical
encoder to virtual encoder.

changes in v4:
	- Fix hw_ctl initialization (Sean)
changes in v5:
	- Update commit text with details on why the change is
	  needed (Sean)

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