Refactor texture coordinate addressing.

Unify address() and addressW() by introducing a new addressing mode.

Change-Id: I09f9cbbe7800cfd5ef737322d680327aeddd27f1
Reviewed-on: https://swiftshader-review.googlesource.com/4714
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Nicolas Capens <capn@google.com>