pinctrl: ralink: mt76x8: fix pinmux function

pinctrl: ralink: mt76x8: fix pinmux function

The current version of the pinctrl driver has some issues:

1. Duplicated "gpio" pmx function

The common code will add a "gpio" pmx functon to every pin group, so
it's not necessary to define a separate "gpio" pmx function in pin
groups.

2. Duplicated pmx function name

There are some same function name in different pin groups, which will
cause some problems. For example, when we want to use PAD_GPIO0 as
refclk output function, the common clk framework code will search the
entire pin function lists, then return the first one matched, in this
case the matched function list only include the PAD_CO_CLKO pin group
because there are three "refclk" pin function, which is added by
refclk_grp, spi_cs1_grp and gpio_grp.

To solve this problem, a simple way is just add a pingrp refix to
function name like mt7620 pinctrl driver does.

3. Useless "-" or "rsvd" functon

It's really unnecessary to add a reserved pin mux function to the
function lists, because we never use it.

Signed-off-by: Weihao Li <cn.liweihao@gmail.com>
Link: https://lore.kernel.org/r/20240527022036.31985-1-user@blabla
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>