leds: lp5523: restore legacy device attributes

git commit db6eaf83
(leds-lp5523: use generic firmware interface) causes an application conflict.
This interface should be maintained for compatibility.

Restored device attributes are 'engineN_mode', 'engineN_load' and
'engineN_leds'. (N = 1, 2 or 3)
A 'selftest' attribute macro is replaced with LP55xx common macro.
Those are accessed when a LED pattern is run by an application.

Use a mutex in lp5523_update_program_memory()
: This function is called when an user-application writes a 'engineN_load' file
or pattern data is loaded from generic firmware interface.
So, writing program memory should be protected.
If an error occurs on accessing this area, just it returns as -EINVAL quickly.
This error code is exact same as old driver function, lp5523_do_store_load()
because it should be kept for an user-application compatibility.
Even the driver is changed, we can use the application without re-compiling
sources.

Reported-by: Pali Rohár <pali.rohar@gmail.com>
Signed-off-by: Milo Kim <milo.kim@ti.com>
Signed-off-by: Bryan Wu <cooloney@gmail.com>