ARM: dts: msm: Add support for Dynamic Fps

Add properties to DSI panel node to support
dynamic FPS. One property is to enable this feature and the
second property is the control when frame rate will be changed.

CRs-Fixed: 488453
Change-Id: I24f6fe88eece327f97212d2aff06100e83164383
Signed-off-by: Chandan Uddaraju <chandanu@codeaurora.org>