bpu: use (27, 12, 12) segmented PC in BPU

[eastonman]

In dhrystone, most high bits of PC is gated.

[XiangShanRobot]

[Generated by IPC robot]
commit: 0023f83

commit	astar	copy_and_run	coremark	gcc	gromacs	lbm	linux	mcf	microbench	milc	namd	povray	wrf	xalancbmk
0023f83	1.821	0.448	2.054	1.173	2.950	2.500	2.291	0.923	1.376	1.265	3.448	2.667	2.398	2.940

master branch:

commit	astar	copy_and_run	coremark	gcc	gromacs	lbm	linux	mcf	microbench	milc	namd	povray	wrf	xalancbmk
071c63e
6b742a1
dc30dd9			2.054	1.173				0.923	1.376		3.448			2.940
cd467f7	1.821	0.448	2.054	1.173	2.950	2.500	2.291	0.923	1.376	1.265	3.448	2.667	2.398	2.940
75b44a5	1.821	0.448	2.054	1.173	2.950	2.500	2.291	0.923	1.376	1.265	3.448	2.667	2.398	2.940
321866f	1.821	0.448	2.054	1.173	2.950	2.500	2.291	0.924	1.376	1.265	3.448	2.667	2.398	2.940
082b30d	1.821	0.448	2.054	1.173	2.950	2.500	2.291	0.923	1.376	1.265	3.448	2.667	2.398	2.940
0e28018	1.823	0.448	2.054	1.172	2.950	2.500	2.292	0.923	1.376	1.265	3.449	2.656	2.398	2.943
df7130a	1.823	0.448	2.054	1.172	2.950	2.500	2.292	0.923	1.376	1.265	3.449	2.656	2.398	2.943