aarch64: Refactor SVE predicated-to-unpredicated splits

aarch64: Refactor SVE predicated-to-unpredicated splits

There are separate patterns for predicated FADD, FSUB, and FMUL.
Previously they each had their own in-built split to convert the
instruction to unpredicated form where appropriate.  However, it's
more convenient for later patches if we use a single separate split
instead.

gcc/
	* config/aarch64/iterators.md (SVE_COND_FP): New code attribute.
	* config/aarch64/aarch64-sve.md: Use a single define_split to
	handle the conversion of predicated FADD, FSUB, and FMUL into
	unpredicated forms.