x86, UV: Set DELIVERY_MODE=4 for vector=NMI_VECTOR in uv_hub_send_ipi()

When sending a NMI_VECTOR IPI using the UV_HUB_IPI_INT register,
we need to ensure the delivery mode field of that register has
NMI delivery selected.

This makes those IPIs true NMIs, instead of flat IPIs. It
matters to reboot sequences and KGDB, both of which use NMI
IPIs.

Signed-off-by: Robin Holt <holt@sgi.com>
Acked-by: Jack Steiner <steiner@sgi.com>
Cc: Martin Hicks <mort@sgi.com>
Cc: <stable@kernel.org>
LKML-Reference: <20091020193620.877322000@alcatraz.americas.sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>