hwc: changes for hdmi hotplug and hpd

This commit has the following changes:
1. Use hdmi switch node for hdmi hotplug
   - uses /devices/virtual/switch/hdmi switch_state to determine
     the hdmi connect/disconnect
   - this switch will be set to 1 on connect and 0 on disconnect
   - on connect, open framebuffer device, will trigger the hdcp
     authentication.
   - the driver will set the hdmi_audio switch to indicate that
     the HDMI sink supports audio
2. Enable HDP on unblank
   - this will resolve the device freeze during the bootup with hdmi
     connected

Change-Id: Id7a656d548a31178e31dcb9aea8acf38a56c9e0c
(cherry picked from commit 953b04b3cbba2f91d25795e5b0560c13d47844b0)
hwc: support WFD external display

Change-Id: I3d24ff1757e79c4b41ff6c6db17d0274cd665671
(cherry picked from commit f8942672226a7af26218aa8d325c1677ae2b83dd)