MIPS: MT: define write_c0_tchalt macro

Define a macro to write to the current TCs TCHalt register. This will be
used by a subsequent patch.
Signed-off-by: Paul Burton <paul.burton@imgtec.com>

arch/mips/include/asm/mipsmtregs.h

@@ -36,6 +36,8 @@
 
 #define read_c0_tcbind()		__read_32bit_c0_register($2, 2)
 
+#define write_c0_tchalt(val)		__write_32bit_c0_register($2, 4, val)
+
 #define read_c0_tccontext()		__read_32bit_c0_register($2, 5)
 #define write_c0_tccontext(val)		__write_32bit_c0_register($2, 5, val)