video :
	use the V4L2_STD macros to select the proper audio setting.

radio :
	add preemphasis ctr.
	test it by the command:
	v4l2-ctl -d /dev/radio0 --set-ctrl=pre_emphasis_settings=1

[mchehab@redhat.com: folded documentation patch]
Signed-off-by: Huang Shijie <shijie8@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>