[POWERPC] virtex bug fix: Use canonical value for AC97 interrupt xparams

The ml300 and ml403 xparameters.h files use different macros for the
AC97 interrupt pin assignments.  This normalizes them to a canonical
value similar to what EDK generates for most other devices.  This is
needed to get ml300 support to compile in arch/ppc.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Acked-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>