arm64: dts: mediatek: cherry: Enable MT6315 regulators on SPMI bus

All machines in the Cherry platform use MT6315 over SPMI: add the
two instances, providing Vbcpu and Vgpu regulators.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Tested-by: Chen-Yu Tsai <wenst@chromium.org>
Link: https://lore.kernel.org/r/20220902081156.38526-8-angelogioacchino.delregno@collabora.com


Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>