bpu: gate s0 registers when s0_stall

[eastonman]

No description provided.

[XiangShanRobot]

[Generated by IPC robot]
commit: 7cb9848

commit	astar	copy_and_run	coremark	gcc	gromacs	lbm	linux	mcf	microbench	milc	namd	povray	wrf	xalancbmk
7cb9848	1.885	0.461	2.100	1.195	2.904	2.175	1.396	0.919	1.421	1.125	3.611	2.666	2.300	3.176

master branch:

commit	astar	copy_and_run	coremark	gcc	gromacs	lbm	linux	mcf	microbench	milc	namd	povray	wrf	xalancbmk
9f659d7	1.875	0.461	2.100	1.203	2.904	2.175	1.397	0.919	1.421	1.125	3.611	2.666	2.300	3.176
1118435	1.878	0.461	2.100	1.213	2.913	2.179	1.397	0.924	1.421	1.127	3.617	2.666	2.302	3.165
31c5451	1.878	0.461	2.100	1.209	2.895	2.179	1.397	0.919	1.421	1.125	3.617	2.666	2.302	3.165
a42a7ff	1.878	0.461	2.100	1.213	2.914	2.181	1.395	0.920	1.421	1.126	3.617	2.659	2.302	3.165
b15e4c0	1.878	0.461	2.100	1.213	2.895	2.181	1.395	0.919	1.421	1.128	3.617	2.659	2.302	3.165
3c5d56a	1.878	0.461	2.100	1.209	2.913	2.182	1.395	0.920	1.421	1.123	3.617	2.660	2.302	3.165
8abe181	1.878	0.461	2.100	1.213	2.895	2.179	1.395	0.919	1.421	1.125	3.617	2.666	2.302	3.165
13156de	1.878	0.461	2.100	1.213	2.895	2.182	1.397	0.919	1.421	1.126	3.617	2.660	2.302	3.165
1fcb3bc	1.878	0.461	2.100	1.211	2.895	2.181	1.395	0.920	1.421	1.123	3.617	2.659	2.302	3.165
f3c16e1	1.878	0.461	2.100	1.213	2.895	2.182	1.396	0.920	1.421	1.126	3.617	2.659	2.302	3.165