[media] media: define Media Controller API when CONFIG_MEDIA_CONTROLLER enabled

Change to define Media Controller API when CONFIG_MEDIA_CONTROLLER
is enabled. Define stubs for CONFIG_MEDIA_CONTROLLER disabled case.
This will help avoid drivers needing to enclose Media Controller
code within ifdef CONFIG_MEDIA_CONTROLLER block.

Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>