i965: Move down genX_upload_sbe in profiles.

Avoid looping over all VARYING_SLOT_MAX urb_setup array
entries from genX_upload_sbe. Prepare an array indirection
to the active entries of urb_setup already in the compile
step. On upload only walk the active arrays.

v2: Use uint8_t to store the attribute numbers.
v3: Change loop to build up the array indirection.
v4: Rebase.
v5: Style fix.

Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Signed-off-by: Mathias Fröhlich <Mathias.Froehlich@web.de>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/308>

src/intel/compiler/brw_compiler.h

@@ -788,6 +788,14 @@ struct brw_wm_prog_data {
     * For varying slots that are not used by the FS, the value is -1.
     */
    int urb_setup[VARYING_SLOT_MAX];
+
+   /**
+    * Cache structure into the urb_setup array above that contains the
+    * attribute numbers of active varyings out of urb_setup.
+    * The actual count is stored in urb_setup_attribs_count.
+    */
+   uint8_t urb_setup_attribs[VARYING_SLOT_MAX];
+   uint8_t urb_setup_attribs_count;
 };
 
 /** Returns the SIMD width corresponding to a given KSP index