Add support for LED APIs for controlling the LED devices. This
API can be used by the LED devices present on the chip and connected
externally via buses like I2C, SPI etc...
Following APIs are currently supported:
1. led_blink
2. led_set_brightness
3. led_on
4. led_off
Driver support using these APIs will be added in subsequent patches.
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
