testsuite: Adjust target requirements for sad-vectorize and signbit.

testsuite: Adjust target requirements for sad-vectorize and signbit.

More testcases with incorrect target selectors.

gcc/testsuite/ChangeLog:

	* gcc.target/powerpc/sad-vectorize-1.c: Remove AIX skip.
	* gcc.target/powerpc/sad-vectorize-2.c: Remove AIX skip.
	* gcc.target/powerpc/sad-vectorize-3.c: Remove target.
	Require p9vector_hw.
	* gcc.target/powerpc/sad-vectorize-4.c: Remove target.
	Require p9vector_hw.
	* gcc.target/powerpc/signbit-1.c: Remove target.
	Require ppc_float128_sw.
	* gcc.target/powerpc/signbit-2.c: Remove target.
	Require ppc_float128_sw.
	* gcc.target/powerpc/signbit-3.c: Remove target.
	Require ppc_float128_sw.