mem-ruby: Sequencer can be used without cache

mem-ruby: Sequencer can be used without cache

Moved the dcache check to the LLSC functions that use it.
This allows a Sequencer to be coupled with a gem5 object
that does not need a cache (as long as it doesn't issue
LLSC instructions).

Also, icache was not used at all so it was removed.

Change-Id: I04bd2711f8d0a7dfc952cff8e0020d2d1881cae1
Signed-off-by: Tiago Mück <tiago.muck@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/31267
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Bradford Beckmann <bradford.beckmann@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>