drm/imx: ipuv3-plane: Configure DMFC wait4eot bit after slots are determined

Just as the function ipu_dmfc_config_wait4eot() tells, the DMFC wait4eot bit
depends on the number of DMFC slots to be used, so it should be called after
the slots are determined in the function ipu_dmfc_alloc_bandwidth().
Based on tests, this patch may eliminate display distortion issue on overlay
plane with small resolutions.  To reproduce the issue, we may run this drm
modetest case - 'modetest -P 19:64x64'.

Signed-off-by: Liu Ying <gnuiyl@gmail.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>