media: ar0521: Setup controls at s_stream time

Setup all the registered controls at s_stream(1) time instead of
manually configure gains.

Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>
Reviewed-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>