anv,hasvk,iris: sampler_prog_key::swizzles is only used on crocus

The field is no longer consumed by brw_complie_* and is instead handled
directly by the crocus driver.  Therefore, it's safe to leave it zero
and not even bother setting it.  This removes our reliance on the
SWIZZLE_* macros in prog_instructions.h.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24288>

src/intel/compiler/brw_compiler.h

@@ -209,6 +209,9 @@ PRAGMA_DIAGNOSTIC_ERROR(-Wpadded)
 struct brw_sampler_prog_key_data {
    /**
     * EXT_texture_swizzle and DEPTH_TEXTURE_MODE swizzles.
+    *
+    * This field is not consumed by the back-end compiler and is only relevant
+    * for the crocus OpenGL driver for Broadwell and earlier hardware.
     */
    uint16_t swizzles[BRW_MAX_SAMPLERS];