Support multiple VCC sources in MediaTek UFS platforms.

Two options are provided and distinguished by specific device tree
attributes as below examples,

[Option 1: By numbering]
mediatek,ufs-vcc-by-num;
vcc-opt1-supply = <&mt6373_vbuck4_ufs>;
vcc-opt2-supply = <&mt6363_vemc>;

[Option 2: By UFS version]
mediatek,ufs-vcc-by-ver;
vcc-ufs3-supply = <&mt6373_vbuck4_ufs>;

Link: https://lore.kernel.org/r/20220616053725.5681-11-stanley.chu@mediatek.comSigned-off-by: Alice Chao <alice.chao@mediatek.com>
Signed-off-by: Peter Wang <peter.wang@mediatek.com>
Signed-off-by: Stanley Chu <stanley.chu@mediatek.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>