scons: Hook in the listnewconfig kconfig helper.

This helper lists config options which are new in the Kconfig and which
are not currently set in the config file.

Change-Id: I0c426d85c0cf0d2bdbac599845669165285a82a0

SConstruct

@@ -261,6 +261,7 @@ Targets:
 
 kconfig_actions = (
     'defconfig',
+    'listnewconfig',
     'menuconfig',
     'setconfig',
 )
@@ -293,6 +294,13 @@ Kconfig tools:
         scons defconfig build/foo/bar build_opts/MIPS
 
 
+        listnewconfig:
+        Lists config options which are new in the Kconfig and which are not
+        currently set in the existing config file.
+
+        scons listnewconfig build/foo/bar
+
+
         menuconfig:
         Opens the menuconfig editor which will let you view and edit config
         values, and view help text. menuconfig runs in text mode.
@@ -831,6 +839,9 @@ for variant_path in variant_paths:
             defconfig_path = makePathAbsolute(kconfig_args[0])
             kconfig.defconfig(env, kconfig_file.abspath,
                     defconfig_path, config_file.abspath)
+        elif kconfig_action == 'listnewconfig':
+            kconfig.listnewconfig(env, kconfig_file.abspath,
+                    config_file.abspath)
         elif kconfig_action == 'menuconfig':
             kconfig.menuconfig(env, kconfig_file.abspath, config_file.abspath,
                     variant_path)