dt-bindings: spmi: document binding for the Mediatek SPMI controller

dt-bindings: spmi: document binding for the Mediatek SPMI controller

This adds documentation for the SPMI controller found on Mediatek SoCs.

Link: https://lore.kernel.org/r/20211119034613.32489-3-james.lo@mediatek.com
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: James Lo <james.lo@mediatek.com>
Signed-off-by: Hsin-Hsiung Wang <hsin-hsiung.wang@mediatek.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>
Link: https://lore.kernel.org/r/20211216190812.1574801-4-sboyd@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>