testsuite: simplify target requirements for various Power9 testcases.

testsuite: simplify target requirements for various Power9 testcases.

This patch removes unnnecessary or simplifies requirements for various
Power9 testcase.

gcc/testsuite/ChangeLog:

	* gcc.target/powerpc/p9-dimode1.c: Remove target.
	* gcc.target/powerpc/p9-dimode2.c: Remove target.
	* gcc.target/powerpc/p9-fpcvt-1.c: Remove target.
	* gcc.target/powerpc/p9-fpcvt-2.c: Require lp64.
	* gcc.target/powerpc/p9-minmax-1.c: Remove target.
	* gcc.target/powerpc/p9-minmax-2.c: Remove target.
	* gcc.target/powerpc/p9-minmax-3.c: Remove target.
	* gcc.target/powerpc/p9-splat-1.c: Require lp64.
	* gcc.target/powerpc/p9-splat-2.c: Remove target.
	* gcc.target/powerpc/p9-splat-3.c: Remove target.
	* gcc.target/powerpc/p9-splat-4.c: Require lp64.
	* gcc.target/powerpc/p9-vbpermd.c: Require lp64.
	* gcc.target/powerpc/p9-vneg.c: Require lp64.
	* gcc.target/powerpc/p9-vparity.c: Require lp64.
	* gcc.target/powerpc/p9-vpermr.c: Require LE.
	* gcc.target/powerpc/p9-xxbr-1.c: Remove target.
	* gcc.target/powerpc/p9-xxbr-2.c: Require lp64.
	* gcc.target/powerpc/p9-xxbr-3.c: Require lp64.