[AArch64] Rewrite vabs<q>_s<8,16,32,64> AdvSIMD intrinsics to fold to tree

gcc/
	* config/aarch64/aarch64-builtins.c
	(aarch64_fold_builtin): Fold abs in all modes.
	* config/aarch64/aarch64-simd-builtins.def
	(abs): Enable for all modes.
	* config/aarch64/arm_neon.h
	(vabs<q>_s<8,16,32,64): Rewrite using builtins.
	(vabs_f64): Add missing intrinsic.

gcc/testsuite/
	* gcc.target/aarch64/vabs_intrinsic_1.c: New file.

From-SVN: r201083