[PowerPC] Call support for fast-isel.

This patch adds fast-isel support for calls (but not intrinsic calls
or varargs calls).  It also removes a badly-formed assert.  There are
some new tests just for calls, and also for folding loads into
arguments on calls to avoid extra extends.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@189701 91177308-0d34-0410-b5e6-96231b3b80d8