MIPS: sgi-ip32: Mask MACE PCI interrupts in CRIME only

Masking PCI interrupts in the MACE PCI control register overwrites the
error and arbitration enables set at init, and a read-modify-write can
hang CRIME 1.1 machines under DMA load. Enable the slot interrupts once
and mask them in CRIME.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Imre Kaloz <kaloz@kernel.org>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>