soc: mediatek: pwrap: add mt6351 driver for mt6797 SoCs

MT6351 is a new power management IC and it is used for mt6797 SoCs. To define
mt6351_regs for pmic register mapping and pmic_mt6351 for
accessing register.

Signed-off-by: Argus Lin <argus.lin@mediatek.com>
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>