Blackfin arch: Add proper -mcpu option according to the cpu and silicon revision configuration

Add silicon revision "any" and "none". Add proper -mcpu option according
to the cpu and silicon revision configuration.

Need update to use latest Blackfin cross compile toolchain.

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