[mlir][NvGpuToNVVM] Fix missing i4 support for nvgpu.mma.sync

This changes adds missing support for the i4 data type. Tests are added
to ensure proper lowering of an nvgpu.mma.sync operation targeting the
16x8x64xi4 and 16x8x32xi4 MMA variants in the NVVM dialect.

Differential Revision: https://reviews.llvm.org/D126092