ART: x86 specific clearing higher bits when converting long to int

The following problem description is taken from
https://android-review.googlesource.com/107261
  If destination and source of long-to-int is the same physical
  register on 64-bit then we do not emit any instructions but
  consider that destination is a 32-bit view of source register.
  As a result high part contains garbage. If the destination is
  used later as index to array access then this garbage is used
  in computation of address because address is 64-bit. For all
  other cases garbage is just ignored.

A generic solution (113023) for all hw platforms was suggested
but rejected later for the sake of HW specific solution:
  https://android-review.googlesource.com/113023
  https://android-review.googlesource.com/114436



This patch is a rework of patch 113023 to stick with x86_64
specific changes: for 64-bit target this patch forces generating
reg-to-reg copy if the src and dest are the same physical
registers. This makes the higher bits be zeroed by 32-bit move
instruction.

Change-Id: Id29af839506ff9319ffba08b2e86e240fef4dafd
Signed-off-by: Serguei Katkov <serguei.i.katkov@intel.com>
Signed-off-by: Yevgeny Rouban <yevgeny.y.rouban@intel.com>