wsi: Better integration interface between WSI and ICD

wsi: Better integration interface between WSI and ICD

Now, ICD provides functions required by WSI as vulkan extensions.
Those extensions might be exposed user if required in the future.
ICD should return the extension functions for all possible query
functions (vk_icdGetInstanceProcAddr and vkGetXXXProcAddress)

Change-Id: I776790598d8d5f3056e5b42c8defb388b8d30e3d