Add vk platform to nullws
Add vk platform to nullws

This CL adds supprt for Vulkan to nullws platform.
In this way deqp-vk can be run on platforms without WSI.

Change-Id: I13d7bc307deeeda3a228b9fa930f7c20950d8ff0

KhronosGroup/Vulkan-CTS,KhronosGroup/VK-GL-CTS,KhronosGroup/Vulkan-CTS,KhronosGroup/Vulkan-CTS,KhronosGroup/VK-GL-CTS,KhronosGroup/VK-GL-CTS,KhronosGroup/VK-GL-CTS,KhronosGroup/Vulkan-CTS,KhronosGroup/VK-GL-CTS,KhronosGroup/Vulkan-CTS,KhronosGroup/Vulkan-CTS,KhronosGroup/VK-GL-CTS