rs6000: Split pattern for TI to V1TI move [PR103124]

This patch defines a new split pattern for TI to V1TI move.  The pattern concatenates two subreg:DI of a TI to a V2DI.  With the pattern, the subreg pass can do register split for TI when there is a TI to V1TI move.

gcc/

	PR target/103124
	* config/rs6000/vsx.md (split pattern for TI to V1TI move): Defined.

gcc/testsuite/

	PR target/103124
	* gcc.target/powerpc/pr103124.c: New testcase.