nir: add shader_info::last_msaa_image

for radeonsi

Acked-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>

src/compiler/shader_info.h

@@ -105,6 +105,8 @@ typedef struct shader_info {
    unsigned num_ssbos;
    /* Number of images used by this shader */
    unsigned num_images;
+   /* Index of the last MSAA image. */
+   int last_msaa_image;
 
    /* Which inputs are actually read */
    uint64_t inputs_read;