nir: add new partially_unrolled bool to nir_loop

In order to stop continuously partially unrolling the same loop
we add the bool partially_unrolled to nir_loop, we add it here
rather than in nir_loop_info because nir_loop_info is only set
via loop analysis and is intended to be cleared before each
analysis. Also nir_loop_info is never cloned.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>

src/compiler/nir/nir.h

@@ -1949,6 +1949,7 @@ typedef struct {
    struct exec_list body; /** < list of nir_cf_node */
 
    nir_loop_info *info;
+   bool partially_unrolled;
 } nir_loop;
 
 /**