soc: mediatek: pwrap: refactor pwrap_init for the various PMIC types

pwrap initialization is highly associated with the base SoC and the
target PMICs, so slight refactorization is made here for allowing
pwrap_init to run on those PMICs with different capability from the
previous MediaTek PMICs and the determination for the enablement of the
pwrap capability depending on PMIC type. Apart from this, the patch
makes the driver more extensible especially when more PMICs join into
the pwrap driver.

Signed-off-by: Chenglin Xu <chenglin.xu@mediatek.com>
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>