Add support for v1i128 type.

Add support for v1i128 type.
The v1i128 type is needed for the quadword add/substract instructions introduced
in POWER8. Futhermore, the PowerPC ABI specifies that parameters of type v1i128
are to be passed in a single vector register, while parameters of type i128 are
passed in pairs of GPRs. Thus, it is necessary to be able to differentiate
between v1i128 and i128 in LLVM.

http://reviews.llvm.org/D8564

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@235198 91177308-0d34-0410-b5e6-96231b3b80d8