gralloc: hdmi cloned mode support

gralloc: hdmi cloned mode support

Patch implements simple support for cloned mode hdmi by introducing
primary and hdmi outputs that are updated respectively.

Current implementation is rather naive and assumes hdmi can drive
same mode as the local lvds. Only cloned mode is supported but can be
extended later to support extended mode when hwcomposer is available
for controlling this behaviour.

HDMI hotplug is implemented as a separate observer thread that
listens to uevents and reads hdmi connection state from there, this
requires switch support from the kernel hdmi driver.

Change-Id: I1d5873214d672563789f4953a892de60539eca88
Signed-off-by: Tapani Pälli <tapani.palli@intel.com>
Signed-off-by: Matt Gumbel <matthew.k.gumbel@linux.intel.com>