PowerPC: Mark patterns as isCodeGenOnly.

There remain a number of patterns that cannot (and should not)
be handled by the asm parser, in particular all the Pseudo patterns.

This commit marks those patterns as isCodeGenOnly.

No change in generated code.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178008 91177308-0d34-0410-b5e6-96231b3b80d8