[MIPS] dump_stack() based on prologue code analysis

Instead of dump all possible address in the stack, unwind the stack frame
based on prologue code analysis, as like as get_wchan() does.  While the
code analysis might fail for some reason, there is a new kernel option
"raw_show_trace" to disable this feature.

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>