pc-bios: petalogix-s3adsp1800.dtb: Use 'xlnx, xps-ethernetlite-2.00.a' instead of 'xlnx, xps-ethernetlite-2.00.b'

For Linux upstream kernel (e.g. 3.17-rc7), the related compatible string
'xlnx,xps-ethernetlite-2.00.a' is supported, but 'b' is not supported,
so change qemu dtb file to match kernel driver.

The related operation for qemu (after this patch):

   yum install libvirt
   yum install tunctl
   tunctl -b
   ip link set tap0 up
   brctl addif virbr0 tap0

   ./configure
   make
   ./microblaze-softmmu/qemu-system-microblaze -M petalogix-s3adsp1800 \
     -kernel ../linux-stable.microblaze/arch/microblaze/boot/linux.bin \
     -no-reboot -append "console=ttyUL0,115200 doreboot" -nographic \
     -net nic,vlan=0,model=xlnx.xps-ethernetlite,macaddr=00:16:35:AF:94:00 \
     -net tap,vlan=0,ifname=tap0,script=no,downscript=no

   in microblaze qemu bash (guest machine):

     ifconfig eth0 add 192.168.122.2 netmask 255.255.255.0
     ifconfig eth0 up

   Then can telnet 192.168.122.2 directly without password from the host
   machine.

The related operation for generating new dtb:

   building Linux kernel firstly, then get dts tool "./scripts/dts/dts".
   "./scripts/dtc/dtc -I dtb -O dts  -o ../work.dts ../qemu/petalogix-s3adsp1800.dtb"
   edit work.dts (replace 'xlnx,xps-ethernetlite-2.00.b')
   "./scripts/dtc/dtc -I dts -O dtb  -o ..qemu/petalogix-s3adsp1800.dtb ../work.dts"

(Since I am not quite sure whether can read this patch or not, I put the
related dtb file in attachment, please check, thanks).

Signed-off-by: Chen Gang <gang.chen.5i5j@gmail.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>