msm_fb: hdmi: Guard HDMI related functions

HDMI dependent functions need to be guarded under HDMI panel
macro to avoid compilation errors for non HDMI builds.

CRs-Fixed: 366864
Change-Id: I02780c167f14e7e44b9f99c121ee2f46a5341051
Signed-off-by: Ajay Singh Parmar <aparmar@codeaurora.org>