arch: Add blackfin CPU choice

This patch adds a Target CPU configuration option and uses it to select
a -m option for gcc.

Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
Acked-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>
1 file changed