ART: Refactor common ELF->InstructionSet code

Move code into instruction_set.h/cc.

Change-Id: I34d5c82791042c68629df84e0f4b9321231d51b9
diff --git a/runtime/arch/instruction_set.h b/runtime/arch/instruction_set.h
index 9135e58..9cfd2eb 100644
--- a/runtime/arch/instruction_set.h
+++ b/runtime/arch/instruction_set.h
@@ -80,6 +80,8 @@
 // Note: Returns kNone when the string cannot be parsed to a known value.
 InstructionSet GetInstructionSetFromString(const char* instruction_set);
 
+InstructionSet GetInstructionSetFromELF(uint16_t e_machine, uint32_t e_flags);
+
 static inline size_t GetInstructionSetPointerSize(InstructionSet isa) {
   switch (isa) {
     case kArm: