powerpc/km82xx: add mgcoge3ne and remove mgcoge2ne support

This patch adds support for the MPC8247 based board mgcoge3ne.
Additionaly mgcoge2ne board supprot was removed, because due
to the mgcoge3ne, this board is obsolete and not longer
maintained.
The board is similar to mgcoge. The difference is that
a NUMONYX flash is used and a different SDRAM (256MB).
Also introduce CONFIG_KM_82XX to collect ppc82xx common
settings and remove staticness from the common set_pin function.

Signed-off-by: Holger Brunck <holger.brunck@keymile.com>
Signed-off-by: Valentin Longchamp <valentin.longchamp@keymile.com>
Acked-by: Heiko Schocher <hs@denx.de>
cc: Wolfgang Denk <wd@denx.de>
cc: Detlev Zundel <dzu@denx.de>