leds: lp55xx: Configure internal charge pump

The LP55xx range of devices have an internal charge pump which
can (automatically) increase the output voltage towards the
LED's, boosting the output voltage to 4.5V.

Implement this option from the devicetree. When the setting
is not present it will operate in automatic mode as before.

Tested on LP55231. Datasheet analysis shows that LP5521, LP5523
and LP8501 are identical in topology and are modified in the
same way.

Signed-off-by: Maarten Zanders <maarten.zanders@mind.be>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20230421075305.37597-3-maarten.zanders@mind.be