gralloc: provide methods for hwc to change handle of a plane

gralloc: provide methods for hwc to change handle of a plane

Patch changes reserve_plane to get id number as additional parameter.
This can be used by hwc to make changes to a particular plane. New
api hwc_set_plane_handle is introduced so that hwc can change the
buffer handle of a plane, this is required because after plane has
been reserved for a particular ui layer, this handle can change as
the layer is typically multibuffered.

Change-Id: I32d711ff3565ae9e8f5b8a6691c22b03a50cefe7
Signed-off-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Topi Pohjolainen <topi.pohjolainen@intel.com>