[Blackfin] arch: theres no need to declare ram{end,start,base} in the head.S files

theres no need to declare ram{end,start,base} in the head.S files
when declaring them with the other memory related variables in setup.c
is so much simpler/nicer

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