ARM: dts: msm: setup external clock sources for HDMI clocks

The HDMI RCGs exported by the MMSS clock controller (MMSS-CC)
can be sourced out of the HDMI PLL which is outside the MMSS-CC.
Set up these external clock sources to point to the HDMI PLL clocks.

CRs-Fixed: 1022772
Change-Id: Ief169f5c456dbdb989788a0147342fe91f0a836f
Signed-off-by: Tatenda Chipeperekwa <tatendac@codeaurora.org>