soc/cores/cpu: add add_sources static method

When creating SoC with multiple sub-SoC already generated, we need an
easy way to add cpu sources.

litex/soc/cores/cpu/lm32/core.py

@@ -56,6 +56,10 @@ class LM32(Module):
         ]
 
         # add verilog sources
+        self.add_sources(platform)
+
+    @staticmethod
+    def add_sources(platform):
         vdir = os.path.join(
             os.path.abspath(os.path.dirname(__file__)), "verilog")
         platform.add_sources(os.path.join(vdir, "submodule", "rtl"),

litex/soc/cores/cpu/mor1kx/core.py

@@ -105,6 +105,10 @@ class MOR1KX(Module):
         ]
 
         # add verilog sources
+        self.add_sources(platform)
+
+    @staticmethod
+    def add_sources(platform):
         vdir = os.path.join(
             os.path.abspath(os.path.dirname(__file__)),
             "verilog", "rtl", "verilog")

litex/soc/cores/cpu/picorv32/core.py

@@ -118,6 +118,10 @@ class PicoRV32(Module):
         ]
 
         # add verilog sources
+        self.add_sources(platform)
+
+    @staticmethod
+    def add_sources(platform):
         vdir = os.path.join(
             os.path.abspath(os.path.dirname(__file__)), "verilog")
         platform.add_source(os.path.join(vdir, "picorv32.v"))

litex/soc/cores/cpu/vexriscv/core.py

@@ -44,7 +44,11 @@ class VexRiscv(Module):
                                   i_dBusWishbone_ACK=d.ack,
                                   i_dBusWishbone_ERR=d.err)
 
-        # add Verilog sources
+        # add verilog sources
+        self.add_sources(platform)
+
+    @staticmethod
+    def add_sources(platform):
         vdir = os.path.join(os.path.abspath(os.path.dirname(__file__)), "verilog")
         platform.add_sources(os.path.join(vdir), "VexRiscv.v")
         platform.add_verilog_include_path(vdir)