testsuite: Enable p9-lxvx-stxvx testcases and fold-vec-extract

testsuite: Enable p9-lxvx-stxvx testcases and fold-vec-extract

This patch enables the p9-lxvx-stxvx testcases with appropriate
requirements.  It also adjusts the expected matching instructions
in the fold-vec-extract testcases for BE.

gcc/testsuite/ChangeLog:

	* gcc.target/powerpc/fold-vec-extract-float.p9.c: rldicl and
	subfic only for target LE.
	* gcc.target/powerpc/fold-vec-extract-longlong.p9.c: xori only
	for target LE.  Adjust mfvsrd and add mfvsrld for BE.
	* gcc.target/powerpc/fold-vec-extract-short.p9.c: vextuhrx for LE.
	vextuhlx for BE.
	* gcc.target/powerpc/p9-lxvx-stxvx-1.c: Remove target.
	* gcc.target/powerpc/p9-lxvx-stxvx-2.c: Remove target.
	* gcc.target/powerpc/p9-lxvx-stxvx-3.c: Remove target. Require
	float128