Recent changes caused that the smmaco4 board now is included in the
boards built by MAKEALL, which revealed that compilation for this
board has been broken for a long time:

mpc5xxx_fec.c:899:2: error: #error fec->xcv_type not initialized.

The board is orphaned.  Drop support for it.

Signed-off-by: Wolfgang Denk <wd@denx.de>