ARM: dts: msm: add display clock nodes for MSM8936

Model the DSI clocks in GCC as a separate device. The byte and pixel clocks
exposed by the DSI PLL device is needed by the GCC DSI clocks. Finally, the
DSI controller can get the clocks exposed by GCC DSI. So, the order of
probes for this to work is GCC->DSI PLL->GCC_MDSS_DSI->DSI controller.

Change-Id: I9c7357211b68b9a02ee2782000b942d98618b178
Signed-off-by: Taniya Das <tdas@codeaurora.org>