configs,stdlib,tests: Remove get_runtime_isa() (#241)

`get_runtime_isa()` has been deprecated for some time. It is a leftover
piece of code from when gem5 was compiled to a single ISA and that ISA
used to configure the simulated system to use that ISA. Since multi-ISA
compilations are possible, `get_runtime_isa()` should not be used.
Unless the gem5 binary is compiled to a single ISA, a failure will
occur.

The new proceedure for specify which ISA to use is by the setting of the
correct `BaseCPU` implementation. E.g., `X86SimpleTimingCPU` of
`ArmO3CPU`.

This patch removes the remaining `get_runtime_isa()` instances and
removes the function itself. The `SimpleCore` class has been updated to
allow for it's CPU factory to return a class, needed by scripts in
"configs/common".

The deprecated functionality in the standard library, which allowed for
the specifying of an ISA when setting up a processor and/or core has
also been removed. Setting an ISA is now manditory.

Fixes #216.

configs/deprecated/example/se.py

@@ -55,7 +55,6 @@ from m5.util import (
 )
 
 from gem5.isas import ISA
-from gem5.runtime import get_runtime_isa
 
 addToPath("../../")
 
@@ -119,7 +118,7 @@ def get_processes(args):
         idx += 1
 
     if args.smt:
-        assert args.cpu_type == "DerivO3CPU"
+        assert isinstance(args.cpu_type, DerivO3CPU)
         return multiprocesses, idx
     else:
         return multiprocesses, 1
@@ -150,7 +149,7 @@ if args.bench:
 
     for app in apps:
         try:
-            if get_runtime_isa() == ISA.ARM:
+            if ObjectList.CPUList().get_isa(args.cpu_type) == ISA.ARM:
                 exec(
                     "workload = %s('arm_%s', 'linux', '%s')"
                     % (app, args.arm_iset, args.spec_input)
@@ -165,7 +164,7 @@ if args.bench:
             multiprocesses.append(workload.makeProcess())
         except:
             print(
-                f"Unable to find workload for {get_runtime_isa().name()}: {app}",
+                f"Unable to find workload for ISA: {app}",
                 file=sys.stderr,
             )
             sys.exit(1)