Add libunwindstack support for Mips and Mips64

This patch requires v3.18 kernel or above, because v3.10 kernel
has a bug (as of 8/1/2017) in the ptrace(GETREGSET) function for mips
and mips64.

Change-Id: I004c1fa190193eebe1c84440b366289122a6bd8a
Signed-off-by: Douglas Leung <douglas.leung@mips.com>
Signed-off-by: Dejan Jovicevic <dejan.jovicevic@mips.com>
diff --git a/libunwindstack/include/unwindstack/Elf.h b/libunwindstack/include/unwindstack/Elf.h
index d27727b..a85e5f4 100644
--- a/libunwindstack/include/unwindstack/Elf.h
+++ b/libunwindstack/include/unwindstack/Elf.h
@@ -42,6 +42,8 @@
   ARCH_ARM64,
   ARCH_X86,
   ARCH_X86_64,
+  ARCH_MIPS,
+  ARCH_MIPS64,
 };
 
 class Elf {