Blackfin arch: remove useless mtd defines in uClinux

dont bother protecting the mtd defines as anything that incorrectly
uses it will get an error during link time anyways ... this prevents
large pointless rebuilds of most files whenever the uclinux mtd map changes state

Signed-off-by: Mike Frysinger <vapier.adi@gmail.com>
Signed-off-by: Bryan Wu <cooloney@kernel.org>