mem: implement lrsc backoff to survive in lr storm

[AugustusWillisWang]

No description provided.

[poemonsense]

[Generated by IPC robot]
commit: fcc3484

commit	astar	coremark	gcc	gromacs	lbm	linux	mcf	microbench	milc	namd	povray	wrf	xalancbmk
fcc3484	1.649	2.048	1.304	2.722	1.763	1.364	0.445	1.447	1.164	3.455	2.407	2.192	1.947

master branch:

commit	astar	coremark	gcc	gromacs	lbm	linux	mcf	microbench	milc	namd	povray	wrf	xalancbmk
67c26c3		2.048	1.309			1.365	0.447	1.447			2.398		1.947
c154173	1.649	2.048	1.313	2.722	1.763	1.365	0.448	1.447	1.164	3.455	2.405	2.196	1.947
9e2176f	1.654	2.048	1.306	2.722	1.763	1.364	0.445	1.447	1.164	3.455	2.397	2.192	1.947
7052722	1.654	2.048	1.311	2.722	1.763	1.365	0.445	1.447	1.164	3.455	2.404	2.193	1.947
3fcd6a8	1.660	2.064	1.317	2.671	1.764	1.366	0.445	1.464	1.160	3.456	2.402	2.196	1.943
a2c8bd3	1.660	2.064	1.317	2.671	1.764	1.368	0.446	1.464	1.161	3.456	2.406	2.195	1.943
58dbdfc	1.659	2.058	1.316	2.671	1.764	1.366	0.445	1.461	1.160	3.456	2.387	2.193	1.943
184d2cf	1.660	2.058	1.318	2.671	1.764	1.364	0.448	1.464	1.160	3.456	2.408	2.192	1.943
026615f	1.659	2.064	1.315	2.671	1.764	1.363	0.448	1.454	1.160	3.456	2.403	2.193	1.943
42b952e	1.656	2.064	1.319	2.671	1.764	1.367	0.445	1.464	1.160	3.456	2.401	2.194	1.943