media: rc: self test for IR encoders and decoders

ir-loopback can transmit IR on one rc device and check the correct
scancode and protocol is decoded on a different rc device. This can be
used to check IR transmission between two rc devices. Using rc-loopback,
we use it to check the IR encoders and decoders themselves.

No hardware is required for this test.

Signed-off-by: Sean Young <sean@mess.org>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Shuah Khan <shuah@kernel.org>