Revert "FMUv2: switch debug console and 2nd GPS"

This reverts commit 9817922bf96611f59552b6a6fd2aebab790135f5.

The commit 9817922bf96611f59552b6a6fd2aebab790135f5 was pushed to master without discussion. I am opening this pull request to revert the change for a discussion of the problem. I am also happy to close the PR again if the outcome is that the pinout swap makes sense.

See also the discussion on: https://groups.google.com/forum/#!topic/drones-discuss/4DnhrOaJWWM

The commit which is reverted in this PR changed the port of the nsh to uart 7 which means that the tx/rx lines on the serial 4/5 df13 connector are on different pins than for instance the tx/rx lines of the mavlink/telemetry (and all other serial) connectors. Instead the pins 2 and 3 on the serial 4/5 connector can be used for a second gps without needing a change on the gps cable.

In my opinion users who are able to set-up a system with a 2nd gps should also be able to swap 2 cables. The nsh is used far more often than a second gps so it should be the default use case (at least for px4 native users, I can see that the change may make sense for APM).