v3d/tex: set up default values for Configuration Parameter 1 if possible

v3d/tex: set up default values for Configuration Parameter 1 if possible

Texture access has three configuration parameters, P0 (texture), P1
(sampler) and P2(lookup). P1 and P2 are optional, but if P2 is needed
(like for example to set the offset for texelFetchOffset), then you
need to set P1.

But until now when setting up P1 we were asking the driver to fill up
the address with the shader state. But in that case we can just fill
that address with the default value NULL.

So let's avoid asking the driver to fill that default values, and do
it directly on the compiler. This is a good-to-have on OpenGL, and
likely would be needed on Vulkan.

Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4962>