dt-bindings: mfd: brcm,bcm59056: Convert to YAML

dt-bindings: mfd: brcm,bcm59056: Convert to YAML

Convert devicetree bindings for the Broadcom BCM59056 PMU MFD from
TXT to YAML format. This patch does not change any functionality;
the bindings remain the same.

The bindings have been split into two parts: the MFD binding and
a separate binding for the regulator node, to simplify the addition
of other models later (which have different regulators).

Signed-off-by: Artur Weber <aweber.kernel@gmail.com>
Reviewed-by: "Rob Herring (Arm)" <robh@kernel.org>
Reviewed-by: Stanislav Jakubek <stano.jakubek@gmail.com>
Link: https://lore.kernel.org/r/20250515-bcm59054-v9-1-14ba0ea2ea5b@gmail.com
Signed-off-by: Lee Jones <lee@kernel.org>