dt-bindings: extcon: maxim,max77843: Add MAX77843 bindings

Document the bindings for MAX77843 MUIC/extcon driver, based on
Exynos5433 TM2 devicetree.  These are neither accurate nor finished
bindings but at least allow parsing existing DTS files.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20220111174805.223732-3-krzysztof.kozlowski@canonical.com