aarch64: Reimplement vabal* intrinsics using builtins

aarch64: Reimplement vabal* intrinsics using builtins

This patch reimplements the vabal intrinsics with builtins.
The RTL pattern is cleaned up to emit the right .8b suffixes for the
inputs (though .16b is also accepted)
and iterate over the right modes. The pattern's only other use is
through the sadv16qi expander, which is adjusted.

I've verified that the codegen for sadv16qi is not worse off.

gcc/ChangeLog:

	* config/aarch64/aarch64-simd-builtins.def (sabal): Define
	builtin.
	(uabal): Likewise.
	* config/aarch64/aarch64-simd.md (aarch64_<sur>abal<mode>_4):
	Rename to...
	(aarch64_<sur>abal<mode>): ... This
	(<sur>sadv16qi): Adust use of the above.
	* config/aarch64/arm_neon.h (vabal_s8): Reimplement using
	builtin.
	(vabal_s16): Likewise.
	(vabal_s32): Likewise.
	(vabal_u8): Likewise.
	(vabal_u16): Likewise.
	(vabal_u32): Likewise.