rs6000: Fix some missing built-in attributes [PR104004]

rs6000: Fix some missing built-in attributes [PR104004]

PR104004 caught some misses on my part in converting to the new built-in
function infrastructure.  In particular, I forgot to mark all of the "nosoft"
built-ins, and one of those should also have been marked "no32bit".

2022-01-27  Bill Schmidt  <wschmidt@linux.ibm.com>

gcc/
	PR target/104004
	* config/rs6000/rs6000-builtins.def (MFFSL): Mark nosoft.
	(MTFSB0): Likewise.
	(MTFSB1): Likewise.
	(SET_FPSCR_RN): Likewise.
	(SET_FPSCR_DRN): Mark nosoft and no32bit.