Adds the data-processing "register-shifted register" form, as
well as the 5-bit immediate shift for mov instructions (which
unfortunately represent this form differently than other instructions).

This CL fixes the ARM integrated assembler to handle all non-V
(i.e. neon) instructions used by the spec2k test suite except:

   rsc: 59 instances.
   rev: 14 instances.

BUG= https://bugs.chromium.org/p/nativeclient/issues/detail?id=4334
R=jpp@chromium.org, stichnot@chromium.org

Review URL: https://codereview.chromium.org/1516063002 .