Add vendor to list of supported partitions in gen_build_prop.py

The kati built vendor.img will still use the kati built vendor
build.prop file, but the soong built vendor.img will use an
autogenerated `build_prop` module for vendor

This CL should be a noop for now

Bug: 374371755
Test: diff in contents for aosp_cf_x86_64_phone https://paste.googleplex.com/5766413037076480
Summary
- timestamp change (expected)
- ro.hwui.use_vulkan changes from "" to false, but I think this is
  functionally equivalent
Test: presubmits

Change-Id: I10bc5b6e8d48b86fa70d5ab0722fee658b1a224a
diff --git a/scripts/gen_build_prop.py b/scripts/gen_build_prop.py
index df9e98d..e0686ed 100644
--- a/scripts/gen_build_prop.py
+++ b/scripts/gen_build_prop.py
@@ -524,7 +524,6 @@
 
   build_prop(args, gen_build_info=False, gen_common_build_props=True, variables=variables)
 
-'''
 def build_vendor_prop(args):
   config = args.config
 
@@ -541,7 +540,6 @@
     ]
 
   build_prop(args, gen_build_info=False, gen_common_build_props=True, variables=variables)
-'''
 
 def build_product_prop(args):
   config = args.config
@@ -608,8 +606,8 @@
         build_odm_prop(args)
       case "product":
         build_product_prop(args)
-      # case "vendor":  # NOT IMPLEMENTED
-      #  build_vendor_prop(args)
+      case "vendor":
+        build_vendor_prop(args)
       case _:
         sys.exit(f"not supported partition {args.partition}")