Added a case in vkCreateImage to explicitly allow for this extension.
Nothing else needs to be done, because Swiftshader doesn't need to do
anything with the format list.

Also expose the extension string in the device extensions.

Bug: b/167557828
Change-Id: I8af6a63068cf1bea28df38738e258a918f0e5582
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/48528Tested-by: Sean Risser <srisser@google.com>
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>