Blackfin: handle reboot anomaly 432

Workaround anomaly 432:
The bfrom_SysControl() firmware function does not clear the SIC_IWR1
register before executing the PLL programming sequence.  Therefore, any
interrupt enabled in the SIC_IWR1 register prior to the call to
bfrom_SysControl() can prematurely terminate the idle sequence required
for the PLL to relock properly. SIC_IWR0 is properly handled.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>