integration/builder: change bios_options to list and add assert for supported options.

litex/soc/integration/builder.py

@@ -62,7 +62,7 @@ class Builder:
         csr_csv          = None,
         csr_svd          = None,
         memory_x         = None,
-        bios_options     = None):
+        bios_options     = []):
         self.soc = soc
 
         # From Python doc: makedirs() will become confused if the path elements to create include '..'
@@ -109,8 +109,8 @@ class Builder:
             for name, src_dir in self.software_packages:
                 define(name.upper() + "_DIRECTORY", src_dir)
 
-            if self.bios_options is not None:
-                for option in self.bios_options:
+            for bios_option in self.bios_options:
+                assert option in ["TERM_NO_HIST", "TERM_MINI", "TERM_NO_COMPLETE"]
                 define(option, "1")
 
             write_to_file(