IFU: cut the number of PC registers

[my-mayfly]

In order to reduce power consumption, some unnecessary PC registers can be trimmed

[XiangShanRobot]

[Generated by IPC robot]
commit: 3096f4a

commit	astar	copy_and_run	coremark	gcc	gromacs	lbm	linux	mcf	microbench	milc	namd	povray	wrf	xalancbmk
3096f4a	1.854	0.450	2.103	1.190	2.468	2.593	2.330	0.961	1.377	1.427	3.123	2.639	2.451	2.960

master branch:

commit	astar	copy_and_run	coremark	gcc	gromacs	lbm	linux	mcf	microbench	milc	namd	povray	wrf	xalancbmk
b628978
5e237ba
363530d
a72b131
05d833a	1.854	0.450	2.103	1.190	2.468	2.593	2.330	0.961	1.377	1.427	3.123	2.639	2.451	2.960
9cb05b4		0.450	2.103				2.330		1.377			2.639
4daa5bf		0.450	2.103	1.190	2.468	2.593	2.329	0.962	1.377	1.427	3.123	2.639		2.960
1e018fb	1.854	0.450	2.103	1.190	2.468	2.593	2.330	0.962	1.377	1.427	3.123	2.639	2.451	2.960
3c71816	1.854	0.450	2.103	1.190	2.468	2.593	2.330	0.962	1.377	1.427	3.123	2.639	2.451	2.960
dfe034b	1.854	0.449	2.103	1.182	2.170	2.181	2.328	0.972	1.386	1.294	2.742	2.592	2.283	2.951

[XiangShanRobot]

[Generated by IPC robot]
commit: 6ee7d91

commit	astar	copy_and_run	coremark	gcc	gromacs	lbm	linux	mcf	microbench	milc	namd	povray	wrf	xalancbmk
6ee7d91	1.854	0.450	2.103	1.190	2.468	2.593	2.330	0.960	1.377	1.427	3.123	2.639	2.451	2.960

master branch:

commit	astar	copy_and_run	coremark	gcc	gromacs	lbm	linux	mcf	microbench	milc	namd	povray	wrf	xalancbmk
c83747b	1.855		2.103	1.177	2.478	2.594		0.957	1.398	1.421	3.117		2.454	2.952
d7a3496	1.855	0.450	2.103	1.177	2.478	2.594	2.332	0.957	1.398	1.421	3.117	2.655	2.454	2.952
5961467	1.855	0.450	2.103	1.177	2.478	2.594	2.333	0.957	1.398	1.421	3.117	2.655	2.454	2.952
4b40434
9eee369	1.854	0.450	2.103	1.190	2.468	2.593	2.330	0.960	1.377	1.427	3.123	2.639	2.451	2.960
006b878	1.854	0.450	2.103	1.190	2.468	2.593	2.330	0.960	1.377	1.427	3.123	2.639	2.451	2.960
7299828	1.854	0.450	2.103	1.190	2.468	2.593	2.330	0.960	1.377	1.427	3.123	2.639	2.451	2.960
0c70648	1.854	0.450	2.103	1.190	2.468	2.593	2.330	0.960	1.377	1.427	3.123	2.639	2.451	2.960
b628978	1.854	0.450	2.103	1.190	2.468	2.593	2.329	0.960	1.377	1.427	3.123	2.639	2.451	2.960
5e237ba		0.450	2.103				2.328		1.377			2.639