[MLIR] Provide bare pointer memref lowering option on gpu-to-nvvm pass

Provide the bare pointer memref lowering option on gpu-to-nvvm pass.
This is needed whenever we lower memrefs on the host function side and
the kernel calls on the host-side (gpu-to-llvm) with the bare ptr
convention. The GPU module side of the lowering should also "align" and
use the bare pointer convention.

Reviewed By: krzysz00

Differential Revision: https://reviews.llvm.org/D152480