sim: Get rid of the IsConforming type trait template.

sim: Get rid of the IsConforming type trait template.

The idea of this template was to distinguish types which should
grow/shrink based on the native size of the ABI in question. Or in other
words, if the ABI was 32 bit, the type should also be 32 bit, or 64 bit
and 64 bit.

Unfortunately, I had intended for Addr to be a conforming type (since
local pointers would be conforming), but uint64_t not to be. Since Addr
is defined as a typedef of uint64_t, the compiler would make *both*
types conforming, giving incorrect behavior on 32 bit systems.

Local pointers will need to be handled in a different way, likely with
the VPtr template, so that they will be treated correctly and not like
an explicitly 64 bit data type.

Change-Id: Idfdd5351260b48bb531a1926b93e0478a297826d
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/40495
Reviewed-by: Gabe Black <gabe.black@gmail.com>
Maintainer: Gabe Black <gabe.black@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>