Include oatdump/Android.mk

oatdump/Android.mk wasn't removed as part of the Android.bp conversion,
as it still contains custom targets like dump-oat-boot.  Add it back to
the subdirs included by art/Android.mk.  Also put back the
ART_DUMP_OAT_PATH variable used by the dump-oat-* targets.

Change-Id: If7086b48e268e3620a3377d0f37442673699ec26
diff --git a/Android.mk b/Android.mk
index 0ed5d87..5a17379 100644
--- a/Android.mk
+++ b/Android.mk
@@ -77,6 +77,7 @@
 # product rules
 
 include $(art_path)/dex2oat/Android.mk
+include $(art_path)/oatdump/Android.mk
 include $(art_path)/imgdiag/Android.mk
 include $(art_path)/patchoat/Android.mk
 include $(art_path)/profman/Android.mk