soc: mediatek: SVS: add debug commands

The purpose of SVS is to help find the suitable voltages
for DVFS. Therefore, if SVS bank voltages are concerned
to be wrong, we can show/disable SVS bank voltages by
this patch.

Signed-off-by: Roger Lu <roger.lu@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Kevin Hilman <khilman@baylibre.com>
Link: https://lore.kernel.org/r/20220516004311.18358-6-roger.lu@mediatek.com


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