[Blackfin] arch: Fix BUG - Enable ISP1362 driver to work ok with BF561

This fixes a bug (zero pointer access) only seen on BF561, during USB
Mass Storage/SCSI Host initialization.

It appears to be related to registering a none existing CPU

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Bryan Wu <bryan.wu@analog.com>