sync: optimize fence merges

If the two fences being merged contain sync_pts from the same timeline,
those two pts will be collapsed into a single pt representing the latter
of the two.

Change-Id: Iced7ebb7e5a17a0c8b1a2969ba3388a4edb9ecaf
Signed-off-by: Erik Gilling <konkers@android.com>
Signed-off-by: Atanas (Tony) Zlatinski <zlatinski@gmail.com>

Conflicts:
	drivers/base/sync.c

Conflicts:
	drivers/base/sync.c