Generate XXSPLTIDP for scalars on power10.

This patch implements XXSPLTIDP support for SF, and DF scalar constants.
The previous patch added support for vector constants.  This patch adds
the support for SFmode and DFmode scalar constants.

I added 2 new tests to test loading up SF and DF scalar constants.

2021-12-15  Michael Meissner  <meissner@the-meissners.org>

gcc/

	* config/rs6000/rs6000.md (UNSPEC_XXSPLTIDP_CONST): New unspec.
	(UNSPEC_XXSPLTIW_CONST): New unspec.
	(movsf_hardfloat): Add support for generating XXSPLTIDP.
	(mov<mode>_hardfloat32): Likewise.
	(mov<mode>_hardfloat64): Likewise.
	(xxspltidp_<mode>_internal): New insns.
	(xxspltiw_<mode>_internal): New insns.
	(splitters for SF/DFmode): Add new splitters for XXSPLTIDP.

gcc/testsuite/

	* gcc.target/powerpc/vec-splat-constant-df.c: New test.
	* gcc.target/powerpc/vec-splat-constant-sf.c: New test.