Currently, the magnification filter information is ignored
by SwiftShader. In order to fix it, the 1st step is simply
to make the sampler aware of this information. After this,
a subsequent cl using the duvdxy computed in computeLod
will choose which filter to use (if they are different).

Change-Id: Idc8636c3d981c944815094f23e443725bed4cf27
Reviewed-on: https://swiftshader-review.googlesource.com/4382Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>