pinctrl: JZ4770: Only enable/disable specified group

The previous code would reconfigure all groups, which is incorrect.
MIPS: JZ4770: Do not register pin mappings as part of the platform

Each individual board should have the opportunity to choose whether
pins are assigned to special purposes or used as GPIO pins.
MIPS: JZ4770: GCW0: Register pinctrl mappings

Only register those pins that we want to use for their non-GPIO
functions.