leds: lp55xx: configure the clock detection

Now LP55xx provides automatic clock detection API, lp55xx_is_extclk_used().
The clock configuration can be done by the driver itself.

(a) Concept
The default value is set by each driver with clock selection.
The internal clock selection bit is updated in case that the external clock
is not detected or clock rate is not 32KHz.

(b) Change on LP55xx platform data
The clock configuration is done automatically, so no need to define
'update_config' in the platform side.
Correlated information are removed in the documentations and header.

(c) Definitions moved from header to driver files
CONFIG register values are moved each driver, LP5521 and LP5562.
Not necessary definitions are removed also.

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