drm/msm/mdp5: dynamically assign hw pipes to planes

(re)assign the hw pipes to planes based on required caps, and to handle
situations where we could not modify an in-use plane (ie. SMP block
reallocation).

This means all planes advertise the superset of formats and properties.
Userspace must (as always) use atomic TEST_ONLY step for atomic updates,
as not all planes may be available for use on every frame.

The mapping of hwpipe to plane is stored in mdp5_state, so that state
updates are atomically committed in the same way that plane/etc state
updates are managed.  This is needed because the mdp5_plane_state keeps
a pointer to the hwpipe, and we don't want global state to become out
of sync with the plane state if an atomic update fails, we hit deadlock/
backoff scenario, etc.  The use of state_lock keeps multiple parallel
updates which both re-assign hwpipes properly serialized.

Signed-off-by: Rob Clark <robdclark@gmail.com>