int4_unpack_conv test of test_gpu_mlir failing on Navi21

[CharlieL7]

Tested on my local system:

[   RUN    ] int4_unpack_convterminate called after throwing an instance of 'migraphx::version_2_11_0::exception'  what():  /codes/1_AMDMIGraphX/src/targets/gpu/mlir.cpp:798: run_backend_pipeline: MLIR backend compilation failed: Error: failed to legalize operation 'amdgpu.raw_buffer_load' that was explicitly marked illegalNote: see current operation: %43 = "amdgpu.raw_buffer_load"(%0, %42) <{boundsCheck = true, operandSegmentSizes = array<i32: 1, 1, 0>}> : (memref<64xi4>, i32) -> i4