scsi: mptfusion: Don't use GFP_ATOMIC for larger DMA allocations

The mpt fusion driver still uses the legacy PCI DMA API which hardcodes
atomic allocations.  This caused the driver to fail to load on some powerpc
VMs with incoherent DMA and small memory sizes.  Switch to use the modern
DMA API and sleeping allocations for large allocations instead.  This is
not a full cleanup of the PCI DMA API usage yet, but just enough to fix the
regression caused by reducing the default atomic pool size.

Link: https://lore.kernel.org/r/20200624165724.1818496-1-hch@lst.de
Fixes: 3ee06a6d

 ("dma-pool: fix too large DMA pools on medium memory size systems")
Reported-by: Guenter Roeck <linux@roeck-us.net>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>