msm: mdss: enable hpd by default if it's not pluggable

If HDMI is configured as non-pluggable, enable the HPD by default
in order to bring up full HDMI functionalities.

Change-Id: Ibbe3b55c5eb93b055455ab461cea11b73a1b514d
Signed-off-by: Vinu Deokaran <vinud@codeaurora.org>