disp: msm: sde: notify frame rate changes through notifier

Currently notifier is only called on power mode changes, but listeners
may also be interested in refresh rate changes.

Change-Id: Ibcbe9f1b402d45d28fcfe40b7cbefddc323cf996
(cherry picked from commit 1730faebcbf4b3b36279cffac69c9d83ad9eaef2)
Signed-off-by: Adrian Salido <salidoa@google.com>
[samtran@codeaurora.org: resolve trivial merge conflicts]
Signed-off-by: Samantha Tran <samtran@codeaurora.org>
Signed-off-by: Dhaval Patel <pdhaval@codeaurora.org>