msm: mdss: add support to program DSI PLL for samarium

Add support for DSI PLL programming on msm samarium.
Specifically, add the structures to define VCO,
dividers, mux, src clock and implement the recommended
PLL power-up sequence for DSI PLL programming on
msmsamarium.

Change-Id: I7a310acd768d4723c4f5aa772f92b7bee9c1afb3
Signed-off-by: Manoj Rao <manojraj@codeaurora.org>