i386: Set SRF, GRR, CWF, GNR, DMR, ARL and PTL issue rate

i386: Set SRF, GRR, CWF, GNR, DMR, ARL and PTL issue rate

Hi,

This patch aims to set SRF issue rate to 4, GNR issue rate to 6. According to
tests about spec2017, the patch has little effect on performance.

For GRR, CWF, DMR, ARL and PTL, the patch set their issue rate to 6. Waiting for
more information to update.

Bootstrapped and regtested on x86_64-linux-pc-gnu, OK for trunk.

BRs,
Lin

gcc/ChangeLog:

	* config/i386/x86-tune-sched.cc (ix86_issue_rate): Set 4 for SRF,
	6 for GRR, GNR, CWF, DMR, ARL, PTL.