drm/msm/hdmi: partial revert for hdmi->power_on changes

hdmi->power_on is not properly set for pluggable platforms
leading to an incorrect return value from cable_status() call.
This partially reverts some changes from two previous commits
touching hdmi->power_on

Change-Id: Icd2d331eaed72950ab027424aaf9e1e6b901a205
Signed-off-by: Navid Bahrani <nbahrani@codeaurora.org>