radv: drop the remaining uses of shader modules

radv: drop the remaining uses of shader modules

With VK_EXT_graphics_pipeline_library, shader modules can be NULL and
be passed via the pNext of VkPipelineShaderStageCreateInfo. To prepare
for this, just store everything we need to radv_pipeline_stage.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15847>