drm/msm/mdp5: Assign a 'right hwpipe' to plane state

If the drm_plane has a source width that's greater than the max width
supported by a SSPP (2560 pixels on 8x96), then we assign a 'r_hwpipe'
to it in mdp5_plane_atomic_check().

TODO: There are a few scenarios where the hwpipe assignments aren't
recommended by HW. For example, an assignment which results in a
drm_plane to of two different types of hwpipes (say RGB0 on left
and DMA1 on right) is not recommended.
Also, hwpipes have a priority mapping, where the higher priority pipe
needs to be staged on left LM, and the lower priority needs to be
staged on the right LM. For example, the priority order for VIG pipes
in decreasing order of priority is VIG0, VIG1, VIG2, and VIG3. So, VIG0
on left and VIG1 on right is a correct configuration, but VIG1 on left
and VIG0 on right isn't. These scenarios are ignored for now for the
sake of simplicity.

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