[llvm][CUDA] Allow NVVMREflect to process OpenCL-specific __nvvm_reflect_ocl()

OpenCL requires constant string arguments to be in a particular address space,
so OpenCL sources can't use the regular `__nvvm_reflect()`.

Allow NVVMReflect pass to accept an Open_CL specific variant with a constant
string in a non-default address space.

Differential Revision: https://reviews.llvm.org/D139213