drm/msm: add support for 5V HPD pin for msm8998

msm8998 needs an additional 5V pin to be
enabled to power the HPD circuit. This change
enables the support for this pin.

Change-Id: I42f91265ce56ff5505e3d9c2382858fe6c1be52b
Signed-off-by: Abhinav Kumar <abhinavk@codeaurora.org>