configs, tests: Ruby.create_system cpus option

This patch is adding an extra parameter to the Ruby.create_system
function. The idea is to remove any assumption about cpu configuration
in the ruby scripts.

At the moment the scripts are assuming a flat list of cpu assigned
to the system object. Unfortunately this is not standardized, as
some systems might empoloy a different layout of cpus, like grouping
them in cluster objects.

With this patch we are allowing client scripts to provide the cpu list
as an extra argument

This has the extra benefit of removing the indexing hack

if len(system.cpu) == 1:

which was present in most scripts

Change-Id: Ibc06b920273cde4f7c394d61c0ca664a7143cd27
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/43287
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>

configs/example/ruby_direct_test.py

@@ -97,7 +97,13 @@ system.clk_domain = SrcClockDomain(clock = options.sys_clock,
 system.cpu = RubyDirectedTester(requests_to_complete = options.requests,
                                 generator = generator)
 
-Ruby.create_system(options, False, system)
+# the ruby tester reuses num_cpus to specify the
+# number of cpu ports connected to the tester object, which
+# is stored in system.cpu. because there is only ever one
+# tester object, num_cpus is not necessarily equal to the
+# size of system.cpu
+cpu_list = [ system.cpu ] * options.num_cpus
+Ruby.create_system(options, False, system, cpus=cpu_list)
 
 # Since Ruby runs at an independent frequency, create a seperate clock
 system.ruby.clk_domain = SrcClockDomain(clock = options.ruby_clock,