regulator: Add BUCK and LDO document for MT6358 and MT6366

Add buck_vcore_sshub and ldo_vsram_others_sshub
regulators to binding document for MT6358 and MT6366.

Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Johnson Wang <johnson.wang@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20220317030402.24894-3-johnson.wang@mediatek.com
Signed-off-by: Mark Brown <broonie@kernel.org>