Add support for EBAZ4205 'Development' Board

References:

- https://github.com/fusesoc/blinky/pull/68/files (EBAZ4205 blinky)
- https://github.com/fusesoc/blinky#ebaz4205-development-board
- https://github.com/olofk/serv/pull/59/files (EBAZ4205 'serv' support)
- Existing 'arty_z7.py' example

Usage:

```
$ pwd
nmigen-boards/nmigen_boards

$ pip3 install --editable "."

$ python3 -m nmigen_boards.ebaz4205
```

At this point, both the LEDs should start blinking.

Author: kholia

nmigen_boards/ebaz4205.py

@@ -0,0 +1,40 @@
+import os
+import subprocess
+
+from nmigen.build import *
+from nmigen.vendor.xilinx_7series import *
+from .resources import *
+
+
+__all__ = ["EBAZ4205Platform"]
+
+
+class EBAZ4205Platform(Xilinx7SeriesPlatform):
+    device      = "xc7z010"
+    package     = "clg400"
+    speed       = "1"
+    default_clk = "clk33_333"
+    resources   = [
+        Resource("clk33_333", 0,
+            Pins("N18", dir="i"), Clock(33.333e6), Attrs(IOSTANDARD="LVCMOS33")),
+
+        *LEDResources(
+            pins="W14 W13",
+            attrs=Attrs(IOSTANDARD="LVCMOS33")),
+
+        UARTResource(0,
+            rx="B19", tx="B20",
+            attrs=Attrs(IOSTANDARD="LVCMOS33")),
+    ]
+    connectors = [
+    ]
+
+    def toolchain_program(self, products, name, **kwargs):
+        xc3sprog = os.environ.get("XC3SPROG", "xc3sprog")
+        with products.extract("{}.bit".format(name)) as bitstream_filename:
+            subprocess.run([xc3sprog, "-c", "jtaghs1_fast", "-p", "1", bitstream_filename], check=True)
+
+
+if __name__ == "__main__":
+    from .test.blinky import *
+    EBAZ4205Platform().build(Blinky(), do_program=True)