msm: mdss: Add support for disabling HDMI while cable is connected

Send disconnect and/or offline event to user-space when user explicitly
asks to stop listening to hpd only if HDMI mirroring is going on. Upon
receiving this event, user-space will trigger power off and HDMI mirroring
will be turned off until user explicitly asks to start listening to HDMI
cable connect.

CRs-Fixed: 409880
Change-Id: I509a9a7ba04066e571b5f762be4804c7dd39c655
Signed-off-by: Ujwal Patel <ujwalp@codeaurora.org>