[media] rc: add support for IR LEDs driven through SPI

[media] rc: add support for IR LEDs driven through SPI

The ir-spi is a simple device driver which supports the
connection between an IR LED and the MOSI line of an SPI device.

The driver, indeed, uses the SPI framework to stream the raw data
provided by userspace through an rc character device. The chardev
is handled by the LIRC framework and its functionality basically
provides:

 - write: the driver gets a pulse/space signal and translates it
   to a binary signal that will be streamed to the IR led through
   the SPI framework.
 - set frequency: sets the frequency whith which the data should
   be sent. This is handle with ioctl with the
   LIRC_SET_SEND_CARRIER flag (as per lirc documentation)
 - set duty cycle: this is also handled with ioctl with the
   LIRC_SET_SEND_DUTY_CYCLE flag. The driver handles duty cycles
   of 50%, 60%, 70%, 75%, 80% and 90%, calculated on 16bit data.

The character device is created under /dev/lircX name, where X is
and ID assigned by the LIRC framework.

Example of usage:

        fd = open("/dev/lirc0", O_RDWR);
        if (fd < 0)
                return -1;

        val = 608000;
        ret = ioctl(fd, LIRC_SET_SEND_CARRIER, &val);
        if (ret < 0)
                return -1;

	val = 60;
        ret = ioctl(fd, LIRC_SET_SEND_DUTY_CYCLE, &val);
        if (ret < 0)
                return -1;

        n = write(fd, buffer, BUF_LEN);
        if (n < 0 || n != BUF_LEN)
                ret = -1;

        close(fd);

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