[gta02-core] ECN update

[Werner Almesberger]

We're making progress on the ECNs :-)

The total number is now 31, with two new ones added today (see
below).

6 are done, 6 deferred or cancelled, one is ready for execution,
and the rest either needs editing or discussing. In fact, many of
the latter ones are already implemented in the schematics, the
ECN just didn't catch up yet.

The newcomers:

- ECN0030: Replace Calypso with Telit GE865
- ECN0031: Use codec to detect jack insertion and HOLD button

We already discussed the modem situation. Telit offer certainly
the path of least resistance and maximum freedom. We still need
to consider a few technical details, though, as described in the
ECN.

ECN0031 is from Joerg's "mega-ECN". We have most of the other
bits already in one form or another, but some of them have to be
spelled out more explicitly or need more technical details. E.g.,
bass fix and proper EMI protection of the jack still need a
component selection.

- Werner