Centralize instruction-set pointer-size, alignment, 64b-width code
in instruction_set.h/cc

This allows to clean up some places that currently make explicit
comparisons.

Change-Id: I0dcc924c52fa53306f706aceea93a2d4a655c5df
diff --git a/compiler/compiled_method.cc b/compiler/compiled_method.cc
index 8e013c1..59ed827 100644
--- a/compiler/compiled_method.cc
+++ b/compiler/compiled_method.cc
@@ -82,21 +82,7 @@
 }
 
 uint32_t CompiledCode::AlignCode(uint32_t offset, InstructionSet instruction_set) {
-  switch (instruction_set) {
-    case kArm:
-    case kThumb2:
-      return RoundUp(offset, kArmAlignment);
-    case kArm64:
-      return RoundUp(offset, kArm64Alignment);
-    case kMips:
-      return RoundUp(offset, kMipsAlignment);
-    case kX86:  // Fall-through.
-    case kX86_64:
-      return RoundUp(offset, kX86Alignment);
-    default:
-      LOG(FATAL) << "Unknown InstructionSet: " << instruction_set;
-      return 0;
-  }
+  return RoundUp(offset, GetInstructionSetAlignment(instruction_set));
 }
 
 size_t CompiledCode::CodeDelta() const {