Update packed_weghts_header to include the new groupwise lowbit header. (#2582)

Summary: Pull Request resolved: #2582

Reviewed By: metascroy

Differential Revision: D77620152

Author: szyszyzys

torchao/experimental/ops/packed_weights_header.h

@@ -18,6 +18,7 @@ enum class PackedWeightsType : uint32_t {
   embedding_xbit_universal = 2,
   linear_8bit_act_xbit_weight_kleidi_ai = 3,
   linear_8bit_act_xbit_weight_lut = 4,
+  groupwise_lowbit_weight_lut = 5,
 };
 
 class PackedWeightsHeader {