We have already iterated over FPList, so there is no need to get
and loop over SEW set again. Or we will generate some useless pseudo
instructions like PseudoXXX_VF16_M1_E64.
We add SEW to FPR_Info so that we can get it later. And we rewrite
FPR_Info to reduce arguments incidentally.
This should reduce the size of files generated by TableGen.