Unifying i387 support

[Eli Zaretskii]

> If one needs to be created, we should follow the layout that the
> FNSAVE instruction stores the data in.

However, note that some registers as stored by FNSAVE might need
further work to present them in human-readable format.  One notable
example is the opcode register which only stores the the lower 11
bits of the opcode.  See my message about the layout of "info float".