[AMD] Fix DeepSeek-V4 FP4 MoE expert memory bloat (#31450)

AITER specific

python/sglang/srt/layers/quantization/fp8.py

@@ -1405,10 +1405,11 @@ class Fp8MoEMethod(FusedMoEMethodBase):
             gu_intv = envs.SGLANG_USE_AITER_MOE_GU_ITLV.get()
             fp4_weight_dtype = _require_fp4_dtype()
 
-            # CK FP4 MoE kernel requires K_packed divisible by 128
-            # (i.e., K_logical divisible by 256).
-            # Pad intermediate_size_per_partition if needed.
-            fp4_k_align = 256
+            # DeepSeek V4 MoE is implemented by the FlyDSL kernel, which supports
+            # tile_k=128, so we only need to pad dim to 128. This lets DeepSeek-V4-Pro
+            # at TP8 skip padding 384 -> 512, reducing routed-expert memory by ~25%.
+            # shuffle_scale also supports non-256 shapes since aiter PR#4130.
+            fp4_k_align = 128
             E, w13_N, w13_K_packed = layer.w13_weight.shape
             _, w2_N, w2_K_packed = layer.w2_weight.shape
             inter_per_part = w13_N // 2