ARM: dts: msm: add ref_clk entries needed for DisplayPort

Add the reference clock entries for Display-Port PLL driver
and Display-Port controller driver nodes. These clocks are needed
before initializing the DP controller and PLL block.

Change-Id: I6df6a254b29d65b91ca4d7744f9163ef9cb6b9ff
Signed-off-by: Chandan Uddaraju <chandanu@codeaurora.org>