driver/net: enic: Try DMA 64 first, then failover to DMA

In servers with more than 1.1 TB of RAM, the existing 40/32 bit DMA
could cause failure as the DMA-able address could go outside the range
addressable using 40/32 bits.

The following patch first tried 64 bit DMA if possible, failover to 32
bit.

Signed-off-by: Sujith Sankar <ssujith@cisco.com>
Signed-off-by: Christian Benvenuti <benve@cisco.com>
Signed-off-by: Govindarajulu Varadarajan <govindarajulu90@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>