v3d/uniforms: update VIEWPORT_X/Y_SCALE uniforms for v71

v3d/uniforms: update VIEWPORT_X/Y_SCALE uniforms for v71

As the packet CLIPPER_XY scaling, this needs to be computed on 1/64ths
of pixel, instead of 1/256ths of pixels.

As this is the usual values that we get from macros, we add manually a
v42 and v71 macro, and define a new helper to get those.

Those granularity values are the same for Vulkan and OpenGL, so
perhaps we should move them to a common place.

As with v3dv, V3D_X macro name is somewhat confusing. It is
specifically created to ask for define values that depends on the
version. But I also felt that V3D_DEFINE_X was too long.

Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25450>