Follow up on Framebuffer Layer query

According to a comment that was added after the cl was landed, depth
and stencil layer queries are valid, so support for it was added.

Here's a link to the original cl:
https://swiftshader-review.googlesource.com/#/c/3541

Change-Id: Ib2eb50fb8cea6537da53bf45b5c7afa1f1a7b61b
Reviewed-on: https://swiftshader-review.googlesource.com/3751
Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>