dt-bindings: mfd: maxim,max77802: Convert to dtschema

Convert the MFD part of Maxim MAX77802 PMIC to DT schema format.  The
example DTS was copied from existing DTS (exynos5800-peach-pi.dts), so
keep the license as GPL-2.0-only.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20220215075344.31421-3-krzysztof.kozlowski@canonical.com