qlcnic: Support SR-IOV enable and disable

o Add QLCNIC_SRIOV to Kconfig.
o Provide PCI sysfs hooks to enable and disable SR-IOV.
o Allow enabling only when CONFIG_QLCNIC_SRIOV is defined.
o qlcnic_sriov_pf.c has all the PF related SR-IOV
  functionality.
o qlcnic_sriov_common.c has VF functionality and SR-IOV
  functionality which is common between VF and PF.
o qlcnic_sriov.h is a common header file for SR-IOV defines.

Signed-off-by: Manish Chopra <manish.chopra@qlogic.com>
Signed-off-by: Sucheta Chakraborty <sucheta.chakraborty@qlogic.com>
Signed-off-by: Rajesh Borundia <rajesh.borundia@qlogic.com>
Signed-off-by: David S. Miller <davem@davemloft.net>