The latest MegaRAID Firmware (for Invader series) has support for 64bit
DMA for both streaming and consistent DMA buffers.  All Ventura series
controller FW always support 64 bit consistent DMA.  Also, on a few
architectures 32bit DMA is not supported.

Current driver always prefers 32bit for consistent DMA and 64bit for
streaming DMA.  This behavior was unintentional and carried forwarded
from legacy controller FW. Need to enhance the driver to support 64bit
consistent DMA buffers based on the firmware capability.

Below is the DMA setting strategy in driver with this patch.  For
Ventura series, always try to set 64bit DMA mask. If it fails fall back
to 32bit DMA mask.  For Invader series and earlier generation
controllers, first try to set to 32bit consistent DMA mask irrespective
of FW capability. This is needed to ensure firmware downgrades do not
break. If 32bit DMA setting fails, check FW capability and try seting to
64bit DMA mask.

There are certain restrictions in the hardware for having all sense
buffers and all reply descriptors to be in the same 4GB memory region.
This limitation is h/w dependent and can not be changed in firmware.
This limitation needs to be taken care in driver while allocating the
buffers.  There was a discussion regarding this - find details at below
link.  https://www.spinics.net/lists/linux-scsi/msg108251.htmlSigned-off-by: Kashyap Desai <kashyap.desai@broadcom.com>
Signed-off-by: Shivasharan S <shivasharan.srikanteshwara@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>