arm64: dts: mediatek: mt8195-cherry: Add MFG0 domain supply

MFG0 is the main power domain for the GPU and its surrounding glue
logic, and has a specific power rail.

Add its power supply on Cherry platforms and remove the now useless
(and wrong) regulator-always-on property from the vbuck1 regulator.

Tested-by: Chen-Yu Tsai <wenst@chromium.org>
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>