This adds some basic fptosi_sat and fptoui_sat target independent cost modelling. The fptosi_sat is modelled as a fmin/fmax to saturate the value, followed by a fp convert. The signed values then have an additional fcmp+select for handling Nan correctly.
The AArch64/Arm costs may be more incorrect, as the instruction exist natively. This can be fixed with target specific cost updates.
Drop the AVX prefix here as well