drm/msm/sde: fix race condition with mdp clk and bw vote update

Current driver has a race condition between the
commit and the validate, where the mdp clock or
the bandwidth can be updated for voting before
the actual configuration is taking place.
This is a problem when the validation is being
done for performance numbers that are lower than
what HW requires in the on-going configuration.
Fix this issue by caching the performance values
in the crtc for all the time that the current hw
configuration is on-going.

Change-Id: I898cfd03b8077a2f0fb7c7c14a0d5ce17f15bde4
Signed-off-by: Ingrid Gallardo <ingridg@codeaurora.org>