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.

Suggested-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Shawn Guo <shawn.guo@freescale.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>