Allow constant element vec_extract to be converted to floating point

Allow constant element vec_extract to be converted to floating point

This patch allows vec_extract of the following types to be converted to
floating point by loading the value directly to the vector register, and then
doing the conversion instead of loading the value to a GPR and then doing a
direct move:

vector int
vector unsigned int
vector unsigned short
vector unsigned char

2023-05-01   Michael Meissner  <meissner@linux.ibm.com>

gcc/

	* config/rs6000/rs6000.md (fp_int_extend): New code attribute.
	* config/rs6000/vsx.md (vsx_extract_v4si_load_to_<uns><mode>): New
	* insn.
	* vsx_extract_<VSX_EXTRACT_I2:mode>_load_to_uns<SFDF:mode>: New insn.

gcc/testsuite/

	* gcc.target/powerpc/vec-extract-mem-char-2.c: New file.
	* gcc.target/powerpc/vec-extract-mem-int-4.c: New file.
	* gcc.target/powerpc/vec-extract-mem-int_5.c: New file.
	* gcc.target/powerpc/vec-extract-mem-short-4.c: New file.