imx-drm: ipuv3-plane: remove function ipu_plane_dpms()
All those ipu_*_put() calls in ipu_plane_dpms() are unnecessary,
because the only occurrence of ipu_plane_dpms() with 'mode' not being
DRM_MODE_DPMS_ON is in function ipu_disable_plane(), which already
has a ipu_plane_put_resources() call to put those ipu resources right
after ipu_plane_dpms().
So with those redundant ipu_*_put() calls removed from ipu_plane_dpms(),
the only left code in the function is ipu_plane_enable|disable(). Thus,
we can just call ipu_plane_enable|disable() as needed directly and
remove the ipu_plane_dpms() function completely.