Improve the performance of bevformer

[Cathy0908]

训练性能：

​ 单机单卡，fp16:

	Official吞吐	EasyCV吞吐	性能提升	环境
bevformer-base	0.727	0.8	10%	A100, batch_size=5, num_worker=8
bevformer-tiny	3.55	9.84	177%	A100, batch_size=32, num_worker=8

推理性能

​ fp32 (精度已对齐)

​ 性能提升：42%

	Name	Backend	Median(FPS)	Mean(FPS)	Median(ms)	Mean(ms)	99th_p	std_dev
0	easycv	TensorRT	3.68697	3.68651	0.271226	0.271259	0.272165	0.000197132
1	easycv script	TensorRT	3.8131	3.79859	0.262254	0.26337	0.295066	0.00577846
2	blade	TensorRT	5.40248	5.23383	0.1851	0.192212	0.261654	0.0163032