[media] doc-rst: document LIRC set carrier ioctls

Put each ioctl on its own page and improve documentation, adding
cross-references for LIRC_SET_REC_CARRIER_RANGE and LIRC_SET_REC_CARRIER,
with can be used together to set a carrier frequency range.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>