Turn on the integrated assembler by default for ppc64 and
ppc64le.

Reviewed by Hal Finkel and Bill Schmidt.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@219129 91177308-0d34-0410-b5e6-96231b3b80d8
Remove cases that are now handled by the parent class implementation.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@219132 91177308-0d34-0410-b5e6-96231b3b80d8