linux-wandboard

sh: Fixup 4K irq stacks.

There was a clobber issue with the register we were saving
the stack in, so we switch to a register that we handle in
the clobber list properly already.

This also follows the x86 changes for allowing the softirq
checks from hardirq context.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>