hwc: Fixes for HDMI primary/external use cases

1. Do not process the display list when the display is not connected.

   This is applicable mainly in the HDMI as primary use case since we
   want to activate the display only when the cable is connected.

2. Do not write to HPD when HDMI is primary

   HPD is always enabled when HDMI is primary, and so we rely on the
   connected state (read from sysfs) to determine if the cable is
   connected or not.

3. Initialize the down scale feature switch

   Initialize down scale feature switch when HDMI is connected but
   before we make the call to modify display attributes.

Change-Id: If2a7c8d7af105a9bbd1b6aeef030ac22b51bd3ef
2 files changed