leds-lp55xx: use lp55xx common init function - platform data

 LP5521/5523 platform data functions are moved to lp55xx common driver.
 New init function, lp55xx_init_device() is created.

Signed-off-by: Milo(Woogyom) Kim <milo.kim@ti.com>
Signed-off-by: Bryan Wu <cooloney@gmail.com>