SVE2: Fix aarch64-sve2-acle-asm tests.
This fixes a logical inconsistency with the SVE2 ACLE tests where the SVE2 tests
are checking for SVE support in the assembler instead of SVE2.
This makes all these tests fail when the user has an SVE enabled assembler but
not an SVE2 one.
gcc/testsuite/ChangeLog:
* lib/target-supports.exp
(check_effective_target_aarch64_asm_sve2_ok): New.
* g++.target/aarch64/sve2/acle/aarch64-sve2-acle-asm.exp: Use it.
* gcc.target/aarch64/sve2/acle/aarch64-sve2-acle-asm.exp: Likewise.