V4L/DVB: ir-core: rename sysfs remote controller class from ir to rc

IR is an alias for Infrared Remote, while RC is an alias for Remote
Controller.

While currently all implementations are with Infrared Remote Controller,
this subsystem is not meant to be used only by IR type of RC's. So,
as discussed on both linux-media and linux-input, the better is to
rename the subsystem as Remote Controller.

While, currently, the only application that uses the /sys/class/irrcv is
ir-keytable application, and its sysfs support works only with the
current linux-next code, it is still possible to change the userspace API
without the risk of breaking applications. So, better to rename this
sooner than later.

Later patches will be needed to rename the files and to move them away
from drivers/media, but this is not a critical issue. So, for now,
let's just change the name of the sysfs class/nodes.

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