[media] DocBook: better document FE_SET_TONE ioctl

Use the proper format for FE_SET_TONE documentation and
improve the documentation.

Keep the enum fe_sec_tone_mode description together with
the ioctl, as both are used together.

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
3 files changed