[MIPS] Stacktrace build-fix and improvement

Fix build error due to stacktrace API change.  Now save_stack_trace()
tries to save all kernel context, including interrupts and exception.
Also some asm code are changed a bit so that we can detect the end of
current context easily.

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/mm/tlbex-fault.S b/arch/mips/mm/tlbex-fault.S
index 9e7f417..e99eaa1 100644
--- a/arch/mips/mm/tlbex-fault.S
+++ b/arch/mips/mm/tlbex-fault.S
@@ -19,8 +19,8 @@
 	move	a0, sp
 	REG_S	a2, PT_BVADDR(sp)
 	li	a1, \write
-	jal	do_page_fault
-	j	ret_from_exception
+	PTR_LA	ra, ret_from_exception
+	j	do_page_fault
 	END(tlb_do_page_fault_\write)
 	.endm