dev: Remove SINIC_VTOPHYS and related code.

dev: Remove SINIC_VTOPHYS and related code.

The code in this #ifdef isn't turned on by anything, and either has or
likely will bitrot, especially since there are no tests to even
determine manually if the code they guard works. They are also
preceeded by panics which say that the code they guard is known not to
work now anyway.

This change also gets rid of TheISA in that file since the only reason
it was around was for vtophys in the guarded code.

Change-Id: I59fd8974d0dd3d7ab0d5a8ccfa6a446d2da41eb0
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/22265
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>
Tested-by: kokoro <noreply+kokoro@google.com>