testsuite, rs6000: Fix some run cases with appropriate _hw

When cleaning up the remaining powerpc_{vsx,altivec}_ok test
cases, I found some dg-do run test cases which should check
for the appropriate {p8vector,vmx}_hw check instead.  This
patch is to adjust them accordingly.

gcc/testsuite/ChangeLog:

	* gcc.target/powerpc/swaps-p8-46.c: Check for p8vector_hw rather than
	powerpc_vsx_ok.
	* gcc.target/powerpc/ppc64-abi-2.c: Check for vmx_hw rather than
	powerpc_altivec_ok.
	* gcc.target/powerpc/pr96139-c.c: Likewise.

gcc/testsuite/gcc.target/powerpc/ppc64-abi-2.c

-/* { dg-do run { target { { powerpc*-*-linux* && lp64 } && powerpc_altivec_ok } } } */
+/* { dg-do run { target { { powerpc*-*-linux* && lp64 } && vmx_hw } } } */
 /* { dg-options "-O2 -fprofile -mprofile-kernel -maltivec -mabi=altivec -mno-pcrel" } */
 #include <stdarg.h>
 #include <signal.h>

gcc/testsuite/gcc.target/powerpc/pr96139-c.c

 /* { dg-do run } */
 /* { dg-options "-O2 -Wall -maltivec" } */
-/* { dg-require-effective-target powerpc_altivec_ok } */
+/* { dg-require-effective-target vmx_hw } */
 
 /*
  * Based on test created by sjmunroe for pr96139

gcc/testsuite/gcc.target/powerpc/swaps-p8-46.c

 /* { dg-do run { target le } } */
-/* { dg-require-effective-target powerpc_vsx_ok } */
+/* { dg-require-effective-target p8vector_hw } */
 /* { dg-options "-mdejagnu-cpu=power8 -mvsx -O2 " } */
 
 typedef __attribute__ ((__aligned__ (8))) unsigned long long __m64;