Add support for Gowin based boards.

Author: whitequark

.env.toolchain

@@ -4,3 +4,4 @@ NEXTPNR_ICE40=yowasp-nextpnr-ice40
 ICEPACK=yowasp-icepack
 NEXTPNR_ECP5=yowasp-nextpnr-ecp5
 ECPPACK=yowasp-ecppack
+NEXTPNR_GOWIN=yowasp-nextpnr-gowin

pdm.lock

@@ -11,9 +11,11 @@ dependencies = [
     "yowasp-yosys",
     "yowasp-nextpnr-ice40",
     "yowasp-nextpnr-ecp5",
+    "yowasp-nextpnr-gowin",
 ]
 
 [tool.pdm.scripts]
 _.env_file = ".env.toolchain"
 build_ice40 = {call = "amaranth_template_fpga:build_ice40()"}
 build_ecp5 = {call = "amaranth_template_fpga:build_ecp5()"}
+build_gowin = {call = "amaranth_template_fpga:build_gowin()"}

pyproject.toml

@@ -1,6 +1,7 @@
 from amaranth import *
 from amaranth_boards.icestick import ICEStickPlatform
 from amaranth_boards.versa_ecp5 import VersaECP5Platform
+from amaranth_boards.tang_nano import TangNanoPlatform
 
 
 class Blinky(Elaboratable):
@@ -25,3 +26,7 @@ def build_ice40():
 
 def build_ecp5():
     VersaECP5Platform().build(Blinky())
+
+
+def build_gowin():
+    TangNanoPlatform().build(Blinky())