rs6000: Various fixes for the new fpscr builtins (PR87509)

rs6000: Various fixes for the new fpscr builtins (PR87509)

With these fixes all testcases test clean for me, both on
powerpc64-linux {-m32,-m64} and on powerpc64le-linux, with all
relevant -mcpu= settings.

	PR target/87509
	* config/rs6000/rs6000-builtin.def (RS6000_BUILTIN_SET_FPSCR_DRN): Use
	RS6000_BTM_DFP.
	* config/rs6000/rs6000.md (rs6000_set_fpscr_rn): Require the operand
	to be DImode.  When using mffscrn, force the operand to a register.

gcc/testsuite/
	PR target/87509
	* gcc.target/powerpc/test_fpscr_drn_builtin.c: Use hard_dfp instead
	of dfp_hw.  Don't include <altivec.h>.
	* gcc.target/powerpc/test_fpscr_drn_builtin_error.c: Ditto.  Require
	lp64.
	* gcc.target/powerpc/test_fpscr_rn_builtin.c: Don't include <altivec.h>.
	* gcc.target/powerpc/test_fpscr_rn_builtin_error.c: Ditto.
	* gcc.target/powerpc/test_mffsl.c: Ditto.

From-SVN: r264863