ixgbe: Make mailbox ops initialization unconditional

There is no actual dependency on initialization of the mailbox ops on
whether SR-IOV is enabled or not and it doesn't hurt to go ahead and
initialize ops unconditionally.  Move the initialization into the device
probe so that the mailbox ops are initialized at the time we have the
board info necessary to do it.

Signed-off-by: Greg Rose <gregory.v.rose@intel.com>
CC: Don Dutile <ddutile@redhat.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Tested-by: Sibai Li <Sibai.li@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>