[AArch64] Merge SVE FMAXNM/FMINNM patterns

[AArch64] Merge SVE FMAXNM/FMINNM patterns

This patch makes us use the same define_insn for both the smax/smin
and fmax/fmin optabs.  It also continues the process started by
the earlier FP unary patch of moving predicated FP patterns from
rtx codes to unspecs.

There's no need to handle the FMAX and FMIN instructions until
the ACLE patch, since we only use FMAXNM and FMINNM at present.

2019-08-07  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* config/aarch64/iterators.md (SVE_COND_FP_MAXMIN_PUBLIC): New
	int iterator.
	(maxmin_uns_op): Handle UNSPEC_COND_FMAXNM and UNSPEC_COND_FMINNM.
	* config/aarch64/aarch64-sve.md
	(<FMAXMIN:su><FMAXMIN:maxmin><SVE_F:mode>3): Rename to...
	(<SVE_COND_FP_MAXMIN_PUBLIC:optab><SVE_F:mode>3): ...this and
	use a single unspec for the rhs.
	(*<su><maxmin><mode>3): Delete.
	(<maxmin_uns><SVE_F:mode>3): Use a single unspec for the rhs.

From-SVN: r274188