pinctrl: imx: add soc specific mux_mode mask and shift property

MX7ULP MUX mode mask and shift bit is different from VF610.
Let's make it a platform specific property for the later easy of
adding MX7ULP support.

One trick in exist code that Vybrid hardcoded the config part
as 0xffff because its mux_config register BIT[15-0] are all configs
part. But it's not true in ULP, so use mux_mask instead to address
the difference.

Cc: Stefan Agner <stefan@agner.ch>
Cc: Bai Ping <ping.bai@nxp.com>
Signed-off-by: Fugang Duan <fugang.duan@nxp.com>
Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
Acked-by: Shawn Guo <shawnguo@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>