[media] docs-rst: Convert CEC uAPI to use C function references

[media] docs-rst: Convert CEC uAPI to use C function references

Name all ioctl references and make them match the ioctls that
are documented. That will improve the cross-reference index,
as it will have all ioctls and syscalls there.

While here, improve the documentation to make them to look more
like the rest of the document.

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