MIPS: mm: Panic if an XPA kernel is run without RIXI

XPA kernels hardcode for the presence of RIXI - the PTE format & its
handling presume RI & XI bits. Make this dependence explicit by panicing
if we run on a system that violates it.

Signed-off-by: Paul Burton <[e-mail]>
Reviewed-by: James Hogan <[e-mail]>
Cc: Paul Gortmaker <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Patchwork: https://patchwork.linux-mips.org/patch/13125/
Signed-off-by: Ralf Baechle <[e-mail]>

arch/mips/mm/tlbex.c

···
 	 */
 	static int run_once = 0;
 
+	if (config_enabled(CONFIG_XPA) && !cpu_has_rixi)
+		panic("Kernels supporting XPA currently require CPUs with RIXI");
+
 	output_pgtable_bits_defines();
 	check_pabits();