[Blackfin] arch: replace implied numbers with real values

replace implied numbers with real values so that strace is able to
calculate things automatically ... the numbers are frozen in our ABI,
so having them based off other __NR_xxx values really doesnt matter
-- no functional changes

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