[AArch64] PR84114: Avoid reassociating FMA

[AArch64] PR84114: Avoid reassociating FMA

As discussed in the PR, the reassociation phase runs before FMAs are formed
and so can significantly reduce FMA opportunities.  Although reassociation
could be switched off, it helps in many cases, so a better alternative is to
only avoid reassociation of floating point additions.  This fixes the testcase
and gives 1% speedup on SPECFP2017, fixing the performance regression.

    gcc/
	PR tree-optimization/84114
	* config/aarch64/aarch64.c (aarch64_reassociation_width)
	Avoid reassociation of FLOAT_MODE addition.

From-SVN: r258248