add initial support for sipeed tang nano 9k board.

boards/sipeed_tangnano9k.py

@@ -0,0 +1,20 @@
+from amaranth_boards.tang_nano_9k import *
+from amaranth.build import *
+
+from top import Top
+
+if __name__ == "__main__":
+    platform = TangNano9kPlatform() # toolchain = (Gowin, Apicula)
+
+    # The platform allows access to the various resources defined by the board
+    # definition from amaranth-boards.
+    led0 = platform.request('led', 0)
+    led1 = platform.request('led', 1)
+    led2 = platform.request('led', 2)
+    led3 = platform.request('led', 3)
+    led4 = platform.request('led', 4)
+    leds = [led0, led1, led2, led3, led4]
+    uart = platform.request('uart', 0)
+
+    platform.build(Top(leds, uart), do_program=True)
+