leds: lp5523: make separate API for loading engine

leds: lp5523: make separate API for loading engine

lp5523_load_engine()
  It is called whenever the operation mode is changed to 'load'.
  It is used for simple operation mode change.
  It will be used when engine mode and LED selection is updated in later patch.

lp5523_load_engine_and_select_page()
  Change the operation mode to 'load' and select program page number.
  This is used for programming a LED pattern at a time.
  So load_engine() is replaced with new API, load_engine_and_select_page()
  in lp5523_firmware_loaded().

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