[media] rc-core: improve ir-kbd-i2c get_key functions

The arguments used for ir-kbd-i2c's get_key() functions are not
really suited for rc-core and the ir_raw/ir_key distinction is
just confusing.

Convert all of them to return a protocol/scancode/toggle triple instead.

Signed-off-by: David Härdeman <david@hardeman.nu>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>