Blackfin arch: fix double fault definition for BF561 core A and core B

VDSP has double fault on core a/b inverted for BF561 -- bit 11 is core a while bit 12 is core b

Signed-off-by: Mike Frysinger <michael.frysinger@analog.com>
Signed-off-by: Bryan Wu <bryan.wu@analog.com>