[MIPS] Provide access functions for c0_badvaddr.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

include/asm-mips/mipsregs.h

@@ -836,6 +836,9 @@ do {									\
 #define read_c0_cache()		__read_32bit_c0_register($7, 0)	/* TX39xx */
 #define write_c0_cache(val)	__write_32bit_c0_register($7, 0, val)
 
+#define read_c0_badvaddr()	__read_ulong_c0_register($8, 0)
+#define write_c0_badvaddr(val)	__write_ulong_c0_register($8, 0, val)
+
 #define read_c0_count()		__read_32bit_c0_register($9, 0)
 #define write_c0_count(val)	__write_32bit_c0_register($9, 0, val)