[media] em28xx-audio: implement em28xx_ops: suspend/resume hooks

Implement em28xx_ops: suspend/resume hooks. em28xx usb driver will
invoke em28xx_ops: suspend and resume hooks for all its extensions
from its suspend() and resume() interfaces.

Signed-off-by: Shuah Khan <shuah.kh@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>