pinctrl: mediatek: introduce multiple memory bases support

Pinctrl design of some mediatek SoC need to access registers that
distribute in multiple memory base address. this patch introduce new
mechanism in mediatek pinctrl driver to support the chips which have
the new design.

This patch add a member 'base_calc' in pinctrl private data, and changed
original 'base' private data to an array of *iomem.

When 'base_calc' attribute is set, it will requests multiplue regs base
from the DT, if 'base_calc' attribute is not set, it only use legacy way
to request single reg resource from the DT.

Signed-off-by: Sam Shih <sam.shih@mediatek.com>