msm: mdss: hdmi: support for hdmi primary

Set HDMI as primary panel if module command line contains hdmi
primary information.

Module cmd line is of format: panel=<lk_cfg>:<pan_intf>:<pan_intf_cfg>
For HDMI as primary, panel_intf would be "hdmi"

Change-Id: I25e37bb019a51c747c6c2a003bcf8d4ccc3a9f91
Signed-off-by: Ajay Singh Parmar <aparmar@codeaurora.org>