mem: Make the FSTranslatingPortProxy stop using vtophys.

mem: Make the FSTranslatingPortProxy stop using vtophys.

That was the only place vtophys was still being used. Instead, use the
data TLB to translate functional, and if that fails try the the
instruction TLB.

Change-Id: Ie5e1e1b5d470f010e25482d785f111dc4292db60
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/26233
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>