media: entity: Add a nop variant of media_entity_cleanup

Add nop variant of media_entity_cleanup. This allows calling
media_entity_cleanup whether or not Media controller is enabled,
simplifying driver code.

Also drop #ifdefs on a few drivers around media_entity_cleanup().

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>