powerpc: mpc85xx: remove stxgp3, stxssa support

These have not been converted to Generic Board, so should be removed.
(See doc/README.generic-board for details.)

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Dan Malek <dan@embeddedalley.com>
22 files changed