ARM: dts: msm: add display clock nodes for MSM8916

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: Ib8f59608021c5193f36d69fdec3d82b2eea70b82
Signed-off-by: Taniya Das <tdas@codeaurora.org>