SVE intrinsics: Fold svaba with op1 all zeros to svabd.

SVE intrinsics: Fold svaba with op1 all zeros to svabd.

Similar to
https://gcc.gnu.org/pipermail/gcc-patches/2024-October/665780.html,
this patch implements folding of svaba to svabd if op1 is all zeros,
resulting in the use of UABD/SABD instructions instead of UABA/SABA.
Tests were added to check the produced assembly for use of UABD/SABD,
also for the _n case.

The patch was bootstrapped and regtested on aarch64-linux-gnu, no regression.
OK for mainline?

Signed-off-by: Jennifer Schmitz <jschmitz@nvidia.com>
gcc/
	* config/aarch64/aarch64-sve-builtins-sve2.cc
	(svaba_impl::fold): Fold svaba to svabd if op1 is all zeros.

gcc/testsuite/
	* gcc.target/aarch64/sve2/acle/asm/aba_s32.c: New tests.
	* gcc.target/aarch64/sve2/acle/asm/aba_s64.c: Likewise.
	* gcc.target/aarch64/sve2/acle/asm/aba_u32.c: Likewise.
	* gcc.target/aarch64/sve2/acle/asm/aba_u64.c: Likewise.