[quantization] Add w8a16 quantization support (#4541)

### What this PR does / why we need it?
related to https://github.com/vllm-project/vllm-ascend/issues/4267

### Does this PR introduce _any_ user-facing change?
support w8a16 quantization now

### How was this patch tested?

- vLLM version: v0.12.0
- vLLM main:
ad32e3e19c

### Test
tested using [aisbench](https://gitee.com/aisbench/benchmark/) with tp2
#### Precision
  | ceval | mmlu | gsm8k
-- | -- | -- | --
bf16 | 90.46 | 89.17 | 96.21
w8a16 | 89.51 | 89.29 | 95.98

#### Performance
  | input_len | output_len | concurrency | TTFT (ms) | TPOT (ms) | TPS
(Total) (tokens/s)
-- | -- | -- | -- | -- | -- | --
bf16 | 2048 | 2048 | 10 | 1911.7136 | 77.988 | 253.9866
w8a16 | 2048 | 2048 | 10 | 2128.6334 | 67.1633 | 293.9117
bf16 | 3500 | 1024 | 10 | 3076.2509 | 84.3525 | 506.949
w8a16 | 3500 | 1024 | 10 | 2685.2031 | 73.015 | 585.4717

---------

Signed-off-by: yyt <yangyit139@gmail.com>
Signed-off-by: TmacAaron <yangyit139@gmail.com>
Co-authored-by: realliujiaxu <realliujiaxu@163.com>

vllm_ascend/quantization/utils.py

@@ -14,6 +14,7 @@ from .w8a8_dynamic import (AscendW8A8DynamicFusedMoEMethod,
                            AscendW8A8DynamicLinearMethod)
 from .w8a8_pdmix import (AscendW8A8PDMixFusedMoeMethod,
                          AscendW8A8PDMixLinearMethod)
+from .w8a16 import AscendW8A16LinearMethod
 
 ASCEND_QUANTIZATION_METHOD_MAP: Dict[str, Dict[str, Type[Any]]] = {
     "W4A16": {
@@ -36,6 +37,9 @@ ASCEND_QUANTIZATION_METHOD_MAP: Dict[str, Dict[str, Type[Any]]] = {
     "W8A8_MIX": {
         "linear": AscendW8A8PDMixLinearMethod,
         "moe": AscendW8A8PDMixFusedMoeMethod,
+    },
+    "W8A16": {
+        "linear": AscendW8A16LinearMethod,
     }
 }