Do not use -msoft-float with intention of disabling FP on aarch64

[kan]

Summary

GNU GCC does does recognise it as a valid option and we already
use -mgeneral-regs-only that has the desired effect.

[emaste]

No objection from me although I wish it were a little less copy-pasta (i.e., could the efi logic exist only in Makefile.inc?)