Zen5 tuning part 4: update reassocation width

Zen5 has 6 instead of 4 ALUs and the integer multiplication can now execute in
3 of them.  FP units can do 2 additions and 2 multiplications with latency 2
and 3.  This patch updates reassociation width accordingly.  This has potential
of increasing register pressure but unlike while benchmarking znver1 tuning
I did not noticed this actually causing problem on spec, so this patch bumps
up reassociation width to 6 for everything except for integer vectors, where
there are 4 units with typical latency of 1.

Bootstrapped/regtested x86_64-linux, comitted.

gcc/ChangeLog:

	* config/i386/i386.cc (ix86_reassociation_width): Update for Znver5.
	* config/i386/x86-tune-costs.h (znver5_costs): Update reassociation
	widths.