[Blackfin] arch: Delete unused (copied from m68k) entries in asm-offsets.c.

Fix some really ancient code that was correct only for the m68k port.
Delete unused (i.e. copied from m68k) entries in asm-offsets.c.

Signed-off-by: Bernd Schmidt <bernds_cb1@t-online.de>
Signed-off-by: Bryan Wu <cooloney@kernel.org>