drm/msm/sde: simplify the sde fence create and trigger logic

Sde fence is supported with only atomic set_property. This
simplifies the requirement to create and trigger fences in
sde driver. The change also avoids the duplicate fence fd
create if existing fd already present on same timeline.

Change-Id: Ibf307a5f597828bf01440687900900ee433dc941
Signed-off-by: Dhaval Patel <pdhaval@codeaurora.org>