Support aiter RMSNorm in AMD (#5510)

Co-authored-by: JieXin Liang <Alcanderian@users.noreply.github.com>

python/sglang/srt/layers/layernorm.py

@@ -20,9 +20,12 @@ import torch
 import torch.nn as nn
 
 from sglang.srt.custom_op import CustomOp
-from sglang.srt.utils import is_cuda
+from sglang.srt.utils import is_cuda, is_hip
+
+logger = logging.getLogger(__name__)
 
 _is_cuda = is_cuda()
+_is_hip = is_hip()
 
 if _is_cuda:
     from sgl_kernel import (
@@ -32,8 +35,20 @@ if _is_cuda:
         rmsnorm,
     )
 
+if _is_hip:
 
-logger = logging.getLogger(__name__)
+    from aiter.ops.rmsnorm import rms_norm, rmsnorm2d_fwd_with_add
+
+    rmsnorm = rms_norm
+
+    def fused_add_rmsnorm(
+        x: torch.Tensor,
+        residual: torch.Tensor,
+        w: torch.Tensor,
+        eps: float,
+    ) -> Tuple[torch.Tensor, torch.Tensor]:
+        rmsnorm2d_fwd_with_add(x, x, residual, residual, w, eps)
+        return x, residual
 
 
 class RMSNorm(CustomOp):
@@ -139,7 +154,7 @@ class Gemma3RMSNorm(nn.Module):
         return f"{tuple(self.weight.shape)}, eps={self.eps}"
 
 
-if not _is_cuda:
+if not (_is_cuda or _is_hip):
     logger.info(
         "sgl-kernel is not available on Non-NV platforms. Fallback to other kernel libraries."
     )