leds: add the sysfs interface into the leds-bd2802 driver for changing wave pattern and led current.

Allow the user application to change the wave pattern and led current by
'wave_pattern' and 'rgb_current' sysfs files.
Signed-off-by: Kim Kyuwon <q1.kim@samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Richard Purdie <rpurdie@linux.intel.com>