`memref.alloc()` on dynamic shape tensor cannot be successfully lowered

[yifeizh2]

Encountered in the following matmul config

module attributes {dlti.target_system_spec = #dlti.target_system_spec<"CPU" : #dlti.target_device_spec<#dlti.dl_entry<"L1_cache_size_in_bytes", 49152 : ui32>, #dlti.dl_entry<"L2_cache_size_in_bytes", 2097152 : ui64>, #dlti.dl_entry<"L3_cache_size_in_bytes", 110100480 : ui64>, #dlti.dl_entry<"num_threads", 56 : i32>, #dlti.dl_entry<"max_vector_width", 512 : i64>>>} {
  func.func @entry(%arg0: tensor<128x512xbf16>, %arg1: tensor<512x1024xbf16>) -> tensor<128x1024xbf16> attributes {llvm.emit_c_interface} {
    %cst = arith.constant 0.000000e+00 : bf16
    %0 = tensor.empty() : tensor<128x1024xbf16>
    %1 = linalg.fill ins(%cst : bf16) outs(%0 : tensor<128x1024xbf16>) -> tensor<128x1024xbf16>
    %2 = linalg.matmul {KBlock = 32 : i32, KThreads = 1 : i32, MBlock = 32 : i32, MThreads = 4 : i32, NBlock = 128 : i32, NThreads = 14 : i32, cast = #linalg.type_fn<cast_signed>, innermostKBlock = 32 : i32, innermostMBlock = 32 : i32, innermostNBlock = 32 : i32} ins(%arg0, %arg1 : tensor<128x512xbf16>, tensor<512x1024xbf16>) outs(%1 : tensor<128x1024xbf16>) -> tensor<128x1024xbf16>
    return %2 : tensor<128x1024xbf16>
  }
}

After one-shot bufferization, we encounter the following

%alloc_3 = memref.alloc(%6) {alignment = 64 : i64} : memref<32x?xf32>

which further being lowered to un-eliminable builtin.unrealized_conversion_cast.

[yifeizh2]

Offline synced with @zhczhong, the issue is caused by brgemm encountering dynamic stride, and we have existing logic in prepareConfigCandidates to filter out such invalid config. Now the same logic is moved to validateConfig to also ensure tuner-generated configs' validity.