liteeth_gen: Add toolchain support/parameter.

LiteX code specialization/generation can be different between toolchain (For the same vendor).
Add parameter to configure it from the .yml file.

examples/udp_s7phyrgmii.yml

@@ -7,6 +7,7 @@
 # PHY ----------------------------------------------------------------------
 phy:         LiteEthS7PHYRGMII
 vendor:      xilinx
+toolchain:   vivado
 # Core ---------------------------------------------------------------------
 clk_freq:    125e6
 core:        udp

examples/wishbone_mii.yml

@@ -7,6 +7,7 @@
 # PHY ----------------------------------------------------------------------
 phy:        LiteEthPHYMII
 vendor:     xilinx
+toolchain:  vivado
 # Core ---------------------------------------------------------------------
 clk_freq:   100e6
 core:       wishbone

liteeth/gen.py

@@ -48,9 +48,11 @@ from liteeth.core import LiteEthUDPIPCore
 # IOs ----------------------------------------------------------------------------------------------
 
 _io = [
+    # Clk / Rst
     ("sys_clock", 0, Pins(1)),
     ("sys_reset", 1, Pins(1)),
 
+    # Interrupt
     ("interrupt", 0, Pins(1)),
 
     # MII PHY Pads
@@ -324,9 +326,11 @@ def main():
     if  "device" not in core_config:
         core_config["device"] = ""
     if core_config["vendor"] == "lattice":
-        platform = LatticePlatform(core_config["device"], io=[], toolchain="diamond")
+        toolchain = core_config.get("toolchain", "diamond")
+        platform  = LatticePlatform(core_config["device"], io=[], toolchain=toolchain)
     elif core_config["vendor"] == "xilinx":
-        platform = XilinxPlatform(core_config["device"], io=[], toolchain="vivado")
+        toolchain = core_config.get("toolchain", "vivado")
+        platform  = XilinxPlatform(core_config["device"], io=[], toolchain=toolchain)
     else:
         raise ValueError("Unsupported vendor: {}".format(core_config["vendor"]))
     platform.add_extension(_io)