Blackfin arch: use "char bfin_board_name[]" rather than "char...

Blackfin arch: use "char bfin_board_name[]" rather than "char *bfin_board_name" per discussion on lkml as the former uses less storage

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