[SCSI] aacraid: remove x86_64 IOMMU dependent code

This may seem like a DILLIGAF, but after chatting with the F/W folks,
there is no harm in dropping the page calculation as denoted in the
enclosed patch for these older adapters in this new age of 4GB+ memory
sticks. Any resource optimization within the old-old-old adapters for
systems with less than 4G of memory is of little consequence. The
existing AAC_QUIRK_31BIT flag in linit.c should look after the rest of
the legacy hardware DMA limitations.

Signed-off-by: Mark Salyzyn <aacraid@adaptec.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>