Change fma_reassoc_width tuning for ampere1

This patch enables reassociation of floating-point additions on ampere1.
This brings about 1% overall benefit on spec2017 fprate cases. (There
are minor regressions in 510.parest_r and 508.namd_r, analyzed here:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110279 .)

gcc/ChangeLog:

	* config/aarch64/aarch64.cc: Change fma_reassoc_width for ampere1.