ARM: dts: armada-385-linksys: group pins in pinctrl

A pin group per node is sufficient, further specialization only serves
as documentation which can be a comment just as well. This simplifies
configuring pins for nodes in dependants.

Also use labels which end up right by the node they are intended for.

Signed-off-by: Ralph Sennhauser <ralph.sennhauser@gmail.com>
Signed-off-by: Imre Kaloz <kaloz@openwrt.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>