Update bswap64-4 test for desired results

Update bswap64-4 test for desired results

Update existing testcase powerpc/bswap64-4.c to
reflect that we generate ldbrx and stdbrx instructions
for newer cpu targets, versus the pair of lwbrx and stwbrx
instructions as seen on previous cpu targets.

2020-03-24  Will Schmidt  <will_schmidt@vnet.ibm.com>

gcc/testsuite/
	* gcc.target/powerpc/bswap64-4.c: Update scan-assembler
	expected results.