leds-lp5521: use generic firmware interface

 LP55xx common driver provides generic firmware interface
 for running a LED pattern.
 LP5521 and LP5523 have many device attributes for running patterns.
 This patch cleans up those complex code.

 Removed device attributes:
 engine1_mode
 engine2_mode
 engine3_mode
 engine1_load
 engine2_load
 engine3_load
 led_pattern

 All device attributes and functions are replaced with two callback functions,
 'firmware_cb' and 'run_engine'.

 New engine functions:
 lp5521_load/stop/run_engine(), lp5521_update_program_memory() and
 lp5521_wait_opmode_done()
Signed-off-by: Milo(Woogyom) Kim <milo.kim@ti.com>
Signed-off-by: Bryan Wu <cooloney@gmail.com>