base: Add some functions to convert floats to bits and vice versa.

base: Add some functions to convert floats to bits and vice versa.

These make it easier to extract the binary representation of floats and
doubles, and given a binary representation convert it back again.

The versions with a size prefix are safer to use since they make it
clear what size inputs/outputs are expected. The versions without are
to make writing generic code easier in case the same code snippet,
templated function, etc., needs to be applied in both circumstances.

Change-Id: Ib1f35a7e88e00806a7c639c211c5699b4af5a472
Reviewed-on: https://gem5-review.googlesource.com/c/14455
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Maintainer: Gabe Black <gabeblack@google.com>