msm: mdss: hdmi: add pll_enable property to support clock recovery

PLL_ENABLE property is used to enable or disable the PLL
update function. With this property PLL update function
only works when PLL_ENABLE is set, and all changes done
to hardware will be discarded once PLL_ENABLE is cleared.

Change-Id: I4a6173de22285b37df1b9371ad29e634ef076edc
Signed-off-by: Narender Ankam <nankam@codeaurora.org>