nds32: eth: Support ftmac100 DM.

Support Andestech eth ftmac100 device tree flow on AG101P/AE3XX platform.
Verification:
 Boot linux kernel via dhcp and bootm ok.

 NDS32 # setenv bootm_size 0x2000000;setenv fdt_high 0x1f00000;
 NDS32 # dhcp 0x600000 10.0.4.97:boomimage-310y-ae300-spi.bin
 BOOTP broadcast 1
 BOOTP broadcast 2
 BOOTP broadcast 3
 BOOTP broadcast 4
 DHCP client bound to address 10.0.4.178 (4899 ms)
	Using mac@e0100000 device
	TFTP from server 10.0.4.97; our IP address is 10.0.4.178
	Filename 'boomimage-310y-ae300-spi.bin'.
	Load address: 0x600000
	Loading: #################################################################
	         #################################################################
	         #################################################################
...
...
	         ###################################
	         233.4 KiB/s
					 done
					 Bytes transferred = 13872076 (d3abcc hex)
	NDS32 # dhcp 0x2000000 10.0.4.97:ae300.dtb
	BOOTP broadcast 1
	BOOTP broadcast 2
	BOOTP broadcast 3
	BOOTP broadcast 4
	DHCP client bound to address 10.0.4.178 (4592 ms)
	Using mac@e0100000 device
	TFTP from server 10.0.4.97; our IP address is 10.0.4.178
	Filename 'ae300.dtb'.
	Load address: 0x2000000
	Loading: #
	         82 KiB/s
					 done
					 Bytes transferred = 2378 (94a hex)
	NDS32 # bootm 0x600000 - 0x2000000
	 Image Name:
	 Created:      2017-03-22   6:52:03 UTC
	 Image Type:   NDS32 Linux Kernel Image (uncompressed)
	 Data Size:    13872012 Bytes = 13.2 MiB
	 Load Address: 0000c000
	 Entry Point:  0000c000
	 Verifying Checksum ... OK
	 Booting using the fdt blob at 0x2000000
	 Loading Kernel Image ... OK
	 Loading Device Tree to 01efc000, end 01eff949 ... OK
	 Linux version 3.10.102-20375-gb0034c1-dirty (rick@app09)
	(gcc version 4.9.3 (2016-07-06_nds32le-linux-glibc-v3_experimental) )
  #293 PREEMPT Wed Mar 22 14:49:28 CST 2017
	CPU: NDS32 N13, AndesCore ID(wb), CPU_VER 0x0d11103f(id 13, rev 17, cfg 4159)
...
...
Signed-off-by: rick <rick@andestech.com>