ramips: replace remaining instances of ralink, port-map

ramips: replace remaining instances of ralink, port-map

Some boards were apparently forgotten when ralink,portmap was renamed
to mediatek,portmap -- probably because they used the long obsolete
ralink,port-map attribute.
If this commit breaks ethernet wan/lan assignment, this is because
the port-map attribute wasn't actually parsed, you'll have to replace
"wllll" by "llllw" in the dts file belonging to that board (and send
a patch doing that!)

Signed-off-by: Daniel Golle <daniel@makrotopia.org>