MLK-20486 drm/imx: ldb: Cleanup enc&conn in ->unbind() if necessary

When the master imx-drm-core binding fails, component_bind_all()
in imx-drm-core ->bind() callback will unbind all bound components
first and then call drm_mode_config_cleanup().  Since the encoder
and connector(located in imx_ldb.imx_ldb_channel) are freed after
the ldb ->unbind() callback, drm_mode_config_cleanup() would
accidentally access the freed encoder and connector again.  To fix
this issue, we should cleanup the encoder and connector, i.e.,
remove them from the global encoder and connector lists, in the
->unbind() callback, so that, drm_mode_config_cleanup() won't find
them again in the lists.  However, we have to make sure they exist
before the cleanup in the ->unbind() callback, because imx-drm-core
->unbind() calls drm_mode_config_cleanup() first and then unbinds
all components via component_unbind_all().  Moreover, the connector
isn't created at the first place if a bridge exists, so the check
before the cleanup makes sense for this reason as well.

Signed-off-by: Liu Ying <victor.liu@nxp.com>