[perf][cpu] Accelerate paged attention GEMMs (QK, PV) on Arm CPUs with NEON (#29193)

Signed-off-by: Fadi Arafeh <fadi.arafeh@arm.com>

csrc/cpu/cpu_attn_impl.hpp

@@ -14,7 +14,7 @@
 #include "utils.hpp"
 
 namespace cpu_attention {
-enum class ISA { AMX, VEC, VEC16 };
+enum class ISA { AMX, VEC, VEC16, NEON };
 
 template <ISA isa, typename scalar_t, int64_t head_dim>
 class AttentionImpl {};
@@ -143,6 +143,12 @@ struct AttentionMetadata {
       case ISA::VEC:
         ss << "VEC, ";
         break;
+      case ISA::VEC16:
+        ss << "VEC16, ";
+        break;
+      case ISA::NEON:
+        ss << "NEON, ";
+        break;
     }
     ss << "workitem_group_num: " << workitem_group_num
        << ", reduction_item_num: " << reduction_item_num