dt-bindings: mfd: max8925: Convert to DT schema format

Convert the binding to DT schema format.

The sub-functions of this MFD device do not have their own compatible
string and are thus described directly in the MFD binding document
after being converted to YAML.

Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20231023131409.1796451-1-sebastian.reichel@collabora.com


Signed-off-by: Lee Jones <lee@kernel.org>