We're supposed to validate the request against what we can actually
support, and return VK_ERROR_FORMAT_NOT_SUPPORTED if not supported.

We had previously only considered total lack of support for the format.

Test: dEQP-VK.texture.shadow.*
Change-Id: Ic5aa81f232bf04583060e88334f7f38dd5f2b2e9
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/31068Tested-by: Chris Forbes <chrisforbes@google.com>
Presubmit-Ready: Chris Forbes <chrisforbes@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>