aarch64: Use RTL builtins for FP ml[as]_n intrinsics

aarch64: Use RTL builtins for FP ml[as]_n intrinsics

Rewrite floating-point vml[as][q]_n Neon intrinsics to use RTL
builtins rather than inline assembly code, allowing for better
scheduling and optimization.

gcc/ChangeLog:

2021-01-18  Jonathan Wright  <jonathan.wright@arm.com>

	* config/aarch64/aarch64-simd-builtins.def: Add
	float_ml[as]_n_builtin generator macros.
	* config/aarch64/aarch64-simd.md (*aarch64_mul3_elt_from_dup<mode>):
	Rename to...
	(mul_n<mode>3): This, and re-order arguments.
	(aarch64_float_mla_n<mode>): Define.
	(aarch64_float_mls_n<mode>): Define.
	* config/aarch64/arm_neon.h (vmla_n_f32): Use RTL builtin
	instead of inline asm.
	(vmlaq_n_f32): Likewise.
	(vmls_n_f32): Likewise.
	(vmlsq_n_f32): Likewise.