drm: xlnx: zynqmp_disp: Skip the modeset for same fb

drm: xlnx: zynqmp_disp: Skip the modeset for same fb

Since the async update creates a separate atomic mode set, there can be
back to back atomic modeset with same fb. If the mode set is applied
twice, it ends up submitting 2 dma transactions, and it results in
jitter. This fixes it by adding the check in plane atomic update,
and using plane mode set in async update.

Signed-off-by: Hyun Kwon <hyun.kwon@xilinx.com>
Tested-by: Preetesh Parekh <preetesh.parekh@xilinx.com>