pinctrl: mediatek: add pinctrl-moore that implements the generic pinctrl dt-bindings

Add a generic driver pinctrl-moore.c for MT762x SoC and any other SoC
that would like to use generic dt-binding. The patch is furtherly
refactored from pinctrl-mt7622.c that totally uses the functions back by
the generic pinctrl core such as GENERIC_PINCONF, GENERIC_PINCTRL_GROUPS,
and GENERIC_PINMUX_FUNCTIONS and its binding also completely follows up
pinctrl-bindings.txt in Documentation/devicetree/bindings/pinctrl/ to
implement.

Signed-off-by: Ryder.Lee <ryder.lee@mediatek.com>
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>