Add special mirroring modes for demonstration purposes.

Assume rotation of HDMI display is portait.
$ adb shell setprop persist.demo.hdmirotation portrait

Don't lock rotation while HDMI is plugged in.
$ adb shell setprop persist.demo.hdmirotationlock false

Hide secondary displays from apps but continue mirroring to them.
$ adb shell setprop persist.demo.singledisplay true

Bug: 7326281
Change-Id: I8f9a3b0bc19821a3a01043b0f516806dac82ce53