dt-bindings: mfd: Add LP87524-Q1

Add the LP87524-Q1 to the bindings along with an example. This is a variant
of the LP87565-Q1 and LP87561-Q1 chips which already have bindings.

Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>