arm: Don't force the ArmISA::TLB in vtophys.cc.

arm: Don't force the ArmISA::TLB in vtophys.cc.

The only reason the TLB pointer is being cast to an ArmISA::TLB is so
that it can call a version of translateFunctional which takes more
arguments, when the standard version of translateFunctional just calls
that underlying function with the same arguments.

Change-Id: I3ffd3a8ecc2dda91ddca77f516e2b2ac7313a227
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/21840
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Maintainer: Giacomo Travaglini <giacomo.travaglini@arm.com>