ramips: drop not existing groups from pinmux

ramips: drop not existing groups from pinmux

RT5350 neither have rgmii nor a mdio pinmux group. MT7628an doesn't
have a jtag group. Having these groups defined might cause a boot
panic.

The pin controller fails to initialise for kernels > 4.9 if invalid
groups are used. If a subsystem references a pin controller
configuration node, it can not find this node and errors out. In worst
case it's the SPI driver which errors out and we have no root
filesystem to mount.

Signed-off-by: Mathias Kresin <dev@kresin.me>