msm: mdss: add support to set the minimum mdp transfer time

For command mode panels current code calculations adjust the mdp
clock rate based in the minimum dsi pixel clock rate. This is
wrong and can lead to power issues since this rate considers
the blanking times which are not required for the mdp clock
calculations.
This change optimize the calculations by only considering the worst
width that could be processed by the mdp without blanking periods
and consider the time expected for the transfer by adjusting
the mdp clock in order to meet the performance requested; this
time can be tuned through the panel configuration.

Change-Id: Ib25df0e8f749d3ffc1d9059d5d7eac27e0f0b81e
Signed-off-by: Ingrid Gallardo <ingridg@codeaurora.org>