[media] rc-core: use an IDA rather than a bitmap

This patch changes rc-core to use the kernel facilities that are already
available for handling unique numbers instead of rolling its own bitmap
stuff.

Signed-off-by: David Härdeman <david@hardeman.nu>
Tested-by: Stefan Lippers-Hollmann <s.l-h@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>