arch: Make the ISA parser always use binary floating point accessors.

arch: Make the ISA parser always use binary floating point accessors.

Any operands which use read_code or write_code would need to start
using the floatToBits and bitsToFloat, but only ARM is using that
mechanism, and not on float operands.

Also I notice that the "predicate" mechanism for operands ignores the
read_code and write_code mechanism, and using both will not work
correctly. This change makes no attempt to fix that problem, but
shouldn't contribute to it either.

Change-Id: I0e3a7f78ed28f40cb66958ef12c32e862950fde0
Reviewed-on: https://gem5-review.googlesource.com/c/14456
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Brandon Potter <Brandon.Potter@amd.com>
Maintainer: Gabe Black <gabeblack@google.com>