media: lirc: implement scancode sending

This introduces a new lirc mode: scancode. Any device which can send raw IR
can now also send scancodes.

int main()
{
	int mode, fd = open("/dev/lirc0", O_RDWR);

        mode = LIRC_MODE_SCANCODE;
	if (ioctl(fd, LIRC_SET_SEND_MODE, &mode)) {
		// kernel too old or lirc does not support transmit
	}
	struct lirc_scancode scancode = {
		.scancode = 0x1e3d,
		.rc_proto = RC_PROTO_RC5,
	};
	write(fd, &scancode, sizeof(scancode));
	close(fd);
}

The other fields of lirc_scancode must be set to 0.

Note that toggle (rc5, rc6) and repeats (nec) are not implemented. Nor is
there a method for holding down a key for a period.

Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>