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>

configs/learning_gem5/part3/test_caches.py

@@ -76,7 +76,6 @@ class TestCacheSystem(RubySystem):
 
         self.sequencers = [RubySequencer(version = i,
                               # I/D cache is combined and grab from ctrl
-                              icache = self.controllers[i].cacheMemory,
                               dcache = self.controllers[i].cacheMemory,
                               clk_domain = self.clk_domain,
                               ) for i in range(num_testers)]