sparc64: Adjust __raw_local_irq_save() to cooperate in NMIs.

If we are in an NMI then doing a plain raw_local_irq_disable() will
write PIL_NORMAL_MAX into %pil, which is lower than PIL_NMI, and thus
we'll re-enable NMIs and recurse.

Doing a simple:

	%pil = %pil | PIL_NORMAL_MAX

does what we want, if we're already at PIL_NMI (15) we leave it at
that setting, else we set it to PIL_NORMAL_MAX (14).

This should get the function tracer working on sparc64.

Signed-off-by: David S. Miller <davem@davemloft.net>