Skip single precision registers in .vsave directives.

In some cases, the code generator will emit s0-s31 in .vsave
directives, and the assembler will refuse to assemble the
code.  This CL backports upstream r161301, which will skip
implicitly defined s0-s31.

------------------------------------------------------------
commit ad62e922
Author: Anton Korobeynikov <asl@math.spbu.ru>
Date:   Sat Aug 4 13:25:58 2012 +0000

    Skip impdef regs during eabi save/restore list emission
    to workaround PR1190

    git-svn-id:
    https://llvm.org/svn/llvm-project/llvm/trunk@161301
    91177308-0d3
------------------------------------------------------------

Change-Id: I1de780922c78933051b6f274daa479b5fdc6e609