[IA64-SGI] Altix only: Fix for sn_dma_flush

The following patch fixes a bug in the SGI Altix sn_dma_flush code.  
sn_dma_flush is broken in 2.6.  The code isn't waiting for the DMA 
data to be flushed out of the PIC ASIC. This patch is based off the 
linux-ia64-test-2.6.12 tree

Signed-off-by: Mike Habeck <habeck@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>