turnip: Add support for fine derivatives.

turnip: Add support for fine derivatives.

This does appear to be the required instruction sequence (dsxpp_1 dst src;
dsxpp_1.p dst src) as dropping either instruction fails the testsuite.

Fixes dEQP-VK.glsl.derivate.*

Reviewed-by: Jonathan Marek <jonathan@marek.ca>
Reviewed-by: Rob Clark <robdclark@chromium.org>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3494>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3494>