[media] media: rc: reduce size of struct ir_raw_event

struct ir_raw_event currently has a size of 12 bytes on most (all?)
architectures. This can be reduced to 8 bytes whilst maintaining
full backwards compatibility.
This saves 2KB in size of struct ir_raw_event_ctrl (as element
kfifo is reduced by 512 * 4 bytes) and it allows to copy the
full struct ir_raw_event with a single 64 bit operation.

Successfully tested with the Nuvoton driver and successfully
compile-tested with the ene_ir driver (as it uses the carrier /
duty_cycle elements).

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>