ART: Clean up arm64 kNumberOfXRegisters usage.

Avoid undefined behavior for arm64 stemming from 1u << 32 in
loops with upper bound kNumberOfXRegisters.

Create iterators for enumerating bits in an integer either
from high to low or from low to high and use them for
<arch>Context::FillCalleeSaves() on all architectures.

Refactor runtime/utils.{h,cc} by moving all bit-fiddling
functions to runtime/base/bit_utils.{h,cc} (together with
the new bit iterators) and all time-related functions to
runtime/base/time_utils.{h,cc}. Improve test coverage and
fix some corner cases for the bit-fiddling functions.

Bug: 13925192

(cherry picked from commit 80afd02024d20e60b197d3adfbb43cc303cf29e0)

Change-Id: I905257a21de90b5860ebe1e39563758f721eab82
diff --git a/runtime/class_linker.cc b/runtime/class_linker.cc
index ef94a30..3133a6d 100644
--- a/runtime/class_linker.cc
+++ b/runtime/class_linker.cc
@@ -30,6 +30,7 @@
 #include "base/logging.h"
 #include "base/scoped_flock.h"
 #include "base/stl_util.h"
+#include "base/time_utils.h"
 #include "base/unix_file/fd_file.h"
 #include "base/value_object.h"
 #include "class_linker-inl.h"