drm/msm/hdmi: Fix connector detect when there is no HPD gpio

Some platforms may not have a HPD gpio line to detect Hot Plug signal from
the connector. They need to rely only on reading REG_HDMI_HPD_INT_STATUS
for HPD.

Modify hdmi_connector_detect logic such that it checks for HPD only using
the status register if there is no HPD gpio.

Signed-off-by: Archit Taneja <architt@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>