hwc: Handle ext display device conn/disconn requests

  On HDMI connection, two uevents are generated
    1."change@/devices/virtual/switch/hdmi"
    2."change@/devices/virtual/switch/hdmi_audio"
  Since we look for "change@/devices/virtual/switch/hdmi",
  Display HAL will process the hotplug request twice.
  This causes regression on HDCP enabled devices.

  Change involves to check for uevent str with
  "change@/devices/virtual/switch/hdmi" to ensures
  that we process connection request only once.

Change-Id: Ica97fd4ef3c8e1064e7d757ab754bb1ee4a3fcaa
CRs-Fixed: 429803
1 file changed