scsi: bnx2i: bnx2fc: add dependency on MMU

Both SCSI_BNX2_ISCSI and SCSI_BNX2X_FCOE select CNIC which it turn
select UIO. The later one is dependant on MMU, so while fixing CNIC
for NOMMU build (by adding explicit dependency on MMU) following
warning shows up:

warning: (SCSI_BNX2_ISCSI && SCSI_BNX2X_FCOE) selects CNIC which has
unmet direct dependencies (NETDEVICES && ETHERNET &&
NET_VENDOR_BROADCOM && PCI && (IPV6 || IPV6=n) && MMU)

Fix it with making SCSI_BNX2_ISCSI and SCSI_BNX2X_FCOE dependant on
MMU.

Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>