bmips: dts: fix pinctrl error

bmips: dts: fix pinctrl error

The kernel logs the error "bcm6368_nand 10000200.nand: there is not valid
maps for state default" on boot and all nand pins show as UNCLAIMED in
sysfs pinmux-pins.

bcm6362.dtsi, bcm6368.dtsi and bcm63268.dtsi use the undocumented property
group which the driver doesn't understand. This has been documented upstream
in commit caf963efd4b0b9ff42ca12e52b8efe277264d35b.

Replacing group with pins allows the nand pins to be properly configured.

Signed-off-by: Kyle Hendry <kylehendrydev@gmail.com>
[add bcm636/bcm6368 and fix commit title]
Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>