Added support for mcpu krait

Added support for mcpu krait

- krait processor currently modeled with the same features as A9.
- Krait processor additionally has VFP4 (fused multiply add/sub)
and hardware division features enabled.
- krait has currently the same Schedule model as A9
- krait cpu flag is not recognized by the GNU assembler yet,
it is replaced with march=armv7-a to avoid a lower march
from being used.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@196619 91177308-0d34-0410-b5e6-96231b3b80d8