drm/msm/dpu: avoid tracking reservations in RM

RM was equipped with reservation tracking structure RSVP
to cache HW reservation of displays for certain clients
where atomic_checks (atomic commit with TEST_ONLY) for all
the displays are called before their respective atomic_commits.
Since DPU doesn't support the sequence anymore, clean up
the support from RM. Replace rsvp with the corresponding
encoder id to tag the HW blocks reserved. It prepares DPU
to get rid of RM altogether and track reservations using
private states.

changes in v2:
	- none

Signed-off-by: Jeykumar Sankaran <jsanka@codeaurora.org>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>