nir: Add new variable modes for ray-tracing

If we were desperate to reduce bits, we could probably also use
shader_in/out for hit attributes as they really are an output from
intersection shaders and read-only in any-hit and closest-hit shaders.
However, other passes such as nir_gether_info like to assume that
anything with nir_var_shader_in/out is indexed using vec4 locations for
interface matching.  It's easier to just add a new variable mode.

Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6479>

src/compiler/nir/nir_serialize.c

@@ -637,9 +637,9 @@ union packed_instr {
       unsigned instr_type:4;
       unsigned deref_type:3;
       unsigned cast_type_same_as_last:1;
-      unsigned modes:12; /* deref_var redefines this */
+      unsigned modes:14; /* deref_var redefines this */
       unsigned packed_src_ssa_16bit:1; /* deref_var redefines this */
-      unsigned _pad:3;  /* deref_var redefines this */
+      unsigned _pad:1;  /* deref_var redefines this */
       unsigned dest:8;
    } deref;
    struct {
@@ -984,7 +984,7 @@ static void
 write_deref(write_ctx *ctx, const nir_deref_instr *deref)
 {
    assert(deref->deref_type < 8);
-   assert(deref->modes < (1 << 12));
+   assert(deref->modes < (1 << 14));
 
    union packed_instr header;
    header.u32 = 0;