leds: introduce lp5521 led driver

LP5521 is a three channel led driver with support
for hardware accelerated patterns (currently used
via lp5521-only sysfs interface).

Currently, it's used on n810 device.

Signed-off-by: Felipe Balbi <felipe.balbi@nokia.com>
Signed-off-by: Richard Purdie <rpurdie@linux.intel.com>