intel/compiler: Mark some methods and parameters const

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4093>

src/intel/compiler/brw_ir_vec4.h

@@ -285,7 +285,7 @@ public:
    bool sol_final_write; /**< gen6: send commit message */
    unsigned sol_vertex; /**< gen6: used for setting dst index in SVB header */
 
-   bool is_send_from_grf();
+   bool is_send_from_grf() const;
    unsigned size_read(unsigned arg) const;
    bool can_reswizzle(const struct gen_device_info *devinfo, int dst_writemask,
                       int swizzle, int swizzle_mask);