Use instruction specific dalvik cache dirs.

- All oat & art files are now placed under /data/dalvik-cache/<isa>/.
- GetDalvikCacheOrDie now requires a mandatory subdirectory argument,
  and is implicitly rooted under /data/.
- Added helper methods to convert InstructionSet enums into strings
  and vice versa.

(cherry picked from commit 2974bc3d8a5d161d449dd66826d668d87bdc3cbe)

Change-Id: Ic7986938e6a7091a2af675ebafec768f7b5fb8cd
diff --git a/runtime/parsed_options.h b/runtime/parsed_options.h
index c02eb1d..e0b0fb5 100644
--- a/runtime/parsed_options.h
+++ b/runtime/parsed_options.h
@@ -85,6 +85,7 @@
   bool profile_start_immediately_;
   ProfilerClockSource profile_clock_source_;
   bool verify_;
+  InstructionSet image_isa_;
 
   static constexpr uint32_t kExplicitNullCheck = 1;
   static constexpr uint32_t kExplicitSuspendCheck = 2;