Blackfin arch: force irq_flags into the .data section

force irq_flags into the .data section by initializing it to
the hardware masks that cannot be disabled.  this way if we
use irq enable/disable functions before the .bss has been
zeroed out (as does our l1 relocate/dma functions), we dont
hit a problem where bss contains bogus crap.

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