v3d/compiler: num_tex_used on v3d_key

We would need on OpenGL to update values for all the textures used. On
OpenGL that value can be always took from the context or the nir
shader, but there are cases on Vulkan that it is not the case, or
would force up to recompute it.

Acked-by: Eric Anholt <eric@anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6766>
2 files changed