Support FP8-E5M2 KV Cache (#2279)

Co-authored-by: zhaoyang <zhao.yang16@zte.com.cn>
Co-authored-by: Zhuohan Li <zhuohan123@gmail.com>

setup.py

@@ -253,6 +253,9 @@ if _is_cuda():
         num_threads = min(os.cpu_count(), nvcc_threads)
         NVCC_FLAGS += ["--threads", str(num_threads)]
 
+    if nvcc_cuda_version >= Version("11.8"):
+        NVCC_FLAGS += ["-DENABLE_FP8_E5M2"]
+
     # changes for punica kernels
     NVCC_FLAGS += torch_cpp_ext.COMMON_NVCC_FLAGS
     REMOVE_NVCC_FLAGS = [