[Quantization][Refactor] use platform dict to choose kernel (#33130)

Signed-off-by: Zhu, Zufang <zufang.zhu@intel.com>
Signed-off-by: zofia <110436990+zufangzhu@users.noreply.github.com>

vllm/model_executor/layers/quantization/kernels/mixed_precision/__init__.py

@@ -33,20 +33,30 @@ from vllm.model_executor.layers.quantization.kernels.mixed_precision.MPLinearKer
 from vllm.model_executor.layers.quantization.kernels.mixed_precision.xpu import (  # noqa: E501
     XPUwNa16LinearKernel,
 )
-from vllm.platforms import current_platform
+from vllm.platforms import PlatformEnum, current_platform
 
 # in priority/performance order (when available)
-_POSSIBLE_KERNELS: list[type[MPLinearKernel]] = [
+_POSSIBLE_KERNELS: dict[PlatformEnum, list[type[MPLinearKernel]]] = {
+    PlatformEnum.CUDA: [
         CutlassW4A8LinearKernel,
         MacheteLinearKernel,
         AllSparkLinearKernel,
         MarlinLinearKernel,
-    Dynamic4bitLinearKernel,
         ConchLinearKernel,
         ExllamaLinearKernel,
+    ],
+    PlatformEnum.ROCM: [
+        ConchLinearKernel,
+        ExllamaLinearKernel,
+    ],
+    PlatformEnum.XPU: [
         XPUwNa16LinearKernel,
+    ],
+    PlatformEnum.CPU: [
+        Dynamic4bitLinearKernel,
         CPUWNA16LinearKernel,
-]
+    ],
+}
 
 
 def choose_mp_linear_kernel(
@@ -78,7 +88,7 @@ def choose_mp_linear_kernel(
             compute_capability = _cc[0] * 10 + _cc[1]
 
     failure_reasons = []
-    for kernel in _POSSIBLE_KERNELS:
+    for kernel in _POSSIBLE_KERNELS[current_platform._enum]:
         if kernel.__name__ in envs.VLLM_DISABLED_KERNELS:
             failure_reasons.append(
                 f" {kernel.__name__} disabled by environment variable"