drivers: ethernet: dwc_xgmac: Added dwc-xgmac

 ethernet driver

This driver is capable of supporting basic features
of synposys dwc-xgmac ethernet MAC IP. Basic features
includes,
1. Tx and Rx, multiple Tx and Rx DMA channels, multiple
   Tx and Rx queues
2. Check Sum Offloading on Tx and Rx for IPv4, IPv6,
   TCP, UDP and ICMP packets
3. 10M/100M/1G speeds, Autonegotiation, Link speed
   configuration, Promiscuous mode, Full/Half
   duplex configuration
4. Added source files for synopsys dwc xgmac mdio driver.
   synopsys dwc xgmac mdio driver fetures includes:
   It supports clause 22 of IEEE 802.3 for ethernet PHY devices
   management.
5. Extended mdio shell support for dwcxgmac mdio driver.

Signed-off-by: Santosh Male <santosh.male@intel.com>