rs6000: Fix vector parity support [PR108699]

The failures on the original failed case builtin-bitops-1.c
and the associated test case pr108699.c here show that the
current support of parity vector mode is wrong on Power.
The hardware insns vprtyb[wdq] which operate on the least
significant bit of each byte per element, they doesn't match
what RTL opcode parity needs, but the current implementation
expands it with them wrongly.

This patch is to fix the handling with one more insn vpopcntb.

	PR target/108699

gcc/ChangeLog:

	* config/rs6000/altivec.md (*p9v_parity<mode>2): Rename to ...
	(rs6000_vprtyb<mode>2): ... this.
	* config/rs6000/rs6000-builtins.def (VPRTYBD): Replace parityv2di2 with
	rs6000_vprtybv2di2.
	(VPRTYBW): Replace parityv4si2 with rs6000_vprtybv4si2.
	(VPRTYBQ): Replace parityv1ti2 with rs6000_vprtybv1ti2.
	* config/rs6000/vector.md (parity<mode>2 with VEC_IP): Expand with
	popcountv16qi2 and the corresponding rs6000_vprtyb<mode>2.

gcc/testsuite/ChangeLog:

	* gcc.target/powerpc/p9-vparity.c: Add scan-assembler-not for vpopcntb
	to distinguish parity byte from parity.
	* gcc.target/powerpc/pr108699.c: New test.