Generate Vulkan framework from Vulkan registry (Part 3)

Instead of using the manually created vulkan.api file for generating the
Vulkan driver framework, we generate it directly from the vulkan registry
(vk.xml)

Bug: 134711355
Test: Build and flash, dEQP tests

Change-Id: I2fc3bc03489bd47c2239eb083c988157979fd674
diff --git a/vulkan/scripts/code_generator.py b/vulkan/scripts/code_generator.py
index 9e14b28..39fedf4 100644
--- a/vulkan/scripts/code_generator.py
+++ b/vulkan/scripts/code_generator.py
@@ -20,6 +20,7 @@
 import generator_common as gencom
 import api_generator as apigen
 import driver_generator as drivergen
+import null_generator as nullgen
 
 if __name__ == '__main__':
   gencom.parseVulkanRegistry()
@@ -27,3 +28,5 @@
   apigen.api_gencpp()
   drivergen.driver_genh()
   drivergen.driver_gencpp()
+  nullgen.null_driver_genh()
+  nullgen.null_driver_gencpp()