testsuite: tree-ssa: Limit targets for vec perm tests

Recently added test cases assume optimized code generation for certain
vectorized code.  However, this optimization might not be applied if
the backends don't support the optimized permuation.

The tests are confirmed to work on aarch64 and x86-64, so this
patch restricts the tests accordingly.

Tested on x86-64.

	PR117728

gcc/testsuite/ChangeLog:

	* gcc.dg/tree-ssa/satd-hadamard.c: Restrict to aarch64 and x86-64.
	* gcc.dg/tree-ssa/vector-8.c: Likewise.
	* gcc.dg/tree-ssa/vector-9.c: Likewise.

Signed-off-by: Christoph Müllner <christoph.muellner@vrull.eu>