Blackfin arch: fix bug - kernel build with write back policy fails to be booted up

Make sure IFLUSH is not the last instruction in the hardware loop to avoid
infinite core stall.

The dcache/icache function that only gets used in writeback mode was putting
IFLUSH as the last instruction in the hardware loop ... we know from design
that this may often lead to inifite core stalling, so switch the FLUSH/IFLUSH
order.

Signed-off-by: Mike Frysinger <vapier.adi@gmail.com>
Signed-off-by: Bryan Wu <cooloney@kernel.org>