NR_IRQS and possible irq values on malta

[Guy Streeter <guy.streeter@gmail.com>]

In mips_pcibios_iack() the irq number is obtained like this:

                irq = GT_READ(GT_PCI0_IACK_OFS);
                irq &= 0xff;

(for coreLV, but similarly for others). This value is used to index
into an array of size NR_IRQS, which is set in mach-generic/irq.h to
128.
 I realize that when things work right, the value of irq isn't likely
to get that big, but it seems to me it should be masked down to 127 or
the NR_IRQS value should be larger. I have no opinion which is the
right thing to do.

--Guy