leds: lp5521: restore legacy device attributes

git commit 9ce7cb17
may cause an application confict, engineN_mode and engineN_load.
This interface should be maintained for compatibility.

Restored device attributes are 'engineN_mode' and 'engineN_load'.
A 'selftest' attribute macro is replaced with LP55xx common macro.

Use a mutex in lp5521_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, lp5521_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.

'led_pattern' attribute is not included
: engineN_mode and _load were created for custom user-application.
'led_pattern' is an exception. I added this attribute not for custom application
but for simple test. Now it is used only in LP5562 driver, not LP5521.

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