[PARISC] Make firmware calls irqsafe-ish...

There's no reason why we shouldn't be using _irqsave instead of
_irq for any of these calls. fwiw, this fixes the
"start_kernel(): bug: interrupts were enabled early" message displayed
on bootup recently.

Signed-off-by: Kyle McMartin <kyle@parisc-linux.org>
Signed-off-by: Matthew Wilcox <matthew@wil.cx>