mdss: display: add clock and bus scaling logic

MDSS hardware supports different bus bandwidth and clock frequencies
depending on the load on the hardware. Add support to driver to
calculate the bus bandwidth and clock frequency requirements and
activate changes before the load on hardware changes.

Change-Id: I9bb5bbc7b3e18fb1a738f527b875506dfa0c5c81
Signed-off-by: Adrian Salido-Moreno <adrianm@codeaurora.org>