[NVPTX] Add lowering of i128 params.

The patch adds support of i128 params lowering. The changes are quite trivial to
support i128 as a "special case" of integer type. With this patch, we lower i128
params the same way as aggregates of size 16 bytes: .param .b8 _ [16].

Currently, NVPTX can't deal with the 128 bit integers:
* in some cases because of failed assertions like
  ValVTs.size() == OutVals.size() && "Bad return value decomposition"
* in other cases emitting PTX with .i128 or .u128 types (which are not valid [1])
  [1] http://docs.nvidia.com/cuda/parallel-thread-execution/index.html#fundamental-types

Differential Revision: https://reviews.llvm.org/D34555
Patch by: Denys Zariaiev (denys.zariaiev@gmail.com)

llvm-svn: 308675