uboot-phytec

MIPS: Remove SLOW_DOWN_IO

CONF_SLOWDOWN_IO is never set for any target, so remove the dead code in
the SLOW_DOWN_IO macro. This is done in preparation for changes to
mips_io_port_base which can be avoided in this path by removing it
entirely.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>