Add crossystem arch (merge from ToT to R12 factory branch_

This CL is a cherry pick of:
 Add dummy crossystem_arch implementation for amd64 (host)
 Change-Id: Ia87cdd9551af1d592ece641c2abcc02db73869e1

 Add default arch to fix compiling outside emake
 Change-Id: I225c2ee7e703aad961c50ec8988ed2466886f266
 Review URL: http://codereview.chromium.org/6820018

 Add crossystem arch (reports x86 or arm, depending on platform)
 Change-Id: I857ead5b108d42195145cdbc5cdafa817f3416b4
 Review URL: http://codereview.chromium.org/6813054

BUG=none # porting since latest factory tools need to use "crossystem arch"
TEST=crossystem arch # see x86

Change-Id: I5049fb7bf88f1cb0cb36ff85813e5a79d2d85d56
Reviewed-on: http://gerrit.chromium.org/gerrit/425
Reviewed-by: Randall Spangler <rspangler@chromium.org>
Tested-by: Hung-Te Lin <hungte@chromium.org>
10 files changed