nir: Rename nir_address_format_vk_index_offset to not be vk

It's just a 32-bit index and offset.  We're going to want to use it in
GL as well so stop talking about Vulkan.

Reviewed-by: Kristian H. Kristensen <hoegsberg@chromium.org>
Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>

src/compiler/nir/nir.h

@@ -3021,9 +3021,9 @@ typedef enum {
 
    /**
     * An address format which is comprised of a vec2 where the first
-    * component is a vulkan descriptor index and the second is an offset.
+    * component is a buffer index and the second is an offset.
     */
-   nir_address_format_vk_index_offset,
+   nir_address_format_32bit_index_offset,
 } nir_address_format;
 bool nir_lower_explicit_io(nir_shader *shader,
                            nir_variable_mode modes,