rs6000: Add TARGET_FLOAT128_HW guard for quad-precision insns

rs6000: Add TARGET_FLOAT128_HW guard for quad-precision insns

gcc/
	* config/rs6000/rs6000.md (floatti<mode>2, floatunsti<mode>2,
	fix_trunc<mode>ti2): Add guard TARGET_FLOAT128_HW.
	* config/rs6000/vsx.md (xsxexpqp_<IEEE128:mode>_<V2DI_DI:mode>,
	xsxsigqp_<IEEE128:mode>_<VEC_TI:mode>, xsiexpqpf_<mode>,
	xsiexpqp_<IEEE128:mode>_<V2DI_DI:mode>, xscmpexpqp_<code>_<mode>,
	*xscmpexpqp, xststdcnegqp_<mode>): Replace guard TARGET_P9_VECTOR
	with TARGET_FLOAT128_HW.
	(xststdc_<mode>, *xststdc_<mode>, isinf<mode>2): Add guard
	TARGET_FLOAT128_HW for the IEEE128 modes.

gcc/testsuite/
	* gcc.target/powerpc/float128-cmp2-runnable.c: Replace
	ppc_float128_sw with ppc_float128_hw and remove p9vector_hw.