net: stmmac: Add support for VLAN promiscuous mode

For dwmac4, enable VLAN promiscuity when MAC controller is requested to
enter promiscuous mode.

Signed-off-by: Chuah, Kim Tatt <kim.tatt.chuah@intel.com>
Signed-off-by: Ong Boon Leong <boon.leong.ong@intel.com>
Signed-off-by: Tan, Tee Min <tee.min.tan@intel.com>
Signed-off-by: Wong Vee Khee <vee.khee.wong@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>