dt-bindings: regulator: mediatek-dvfsrc: Add MT6893 support

dt-bindings: regulator: mediatek-dvfsrc: Add MT6893 support

Add a compatible for the MediaTek Dimensity 1200 (MT6893) SoC's
regulators over DVFSRC.
This SoC uses different values for the vsel, hence it is not
compatible with the currently supported ones.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Acked-by: "Rob Herring (Arm)" <robh@kernel.org>
Link: https://patch.msgid.link/20250623120144.109359-2-angelogioacchino.delregno@collabora.com
Signed-off-by: Mark Brown <broonie@kernel.org>