[test] Add status-file variable mips_arch_variant.

Introducing a new status-file variable: mips_arch_variant. With this
variable, in status files will be possible to define selections which
are based on MIPS architecture revisions/variants.

TEST=
BUG=

Change-Id: Ifd682552db2f26be4e56dc94ad50bed063ff14c5
Reviewed-on: https://chromium-review.googlesource.com/941212Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Ivica Bogosavljevic <ivica.bogosavljevic@mips.com>
Cr-Commit-Position: refs/heads/master@{#51647}

tools/testrunner/base_runner.py

@@ -599,6 +599,10 @@ class BaseTestRunner(object):
       self.build_config.mips_arch_variant == "r6" and
       self.build_config.mips_use_msa)
 
+    mips_arch_variant = (
+      self.build_config.arch in ['mipsel', 'mips', 'mips64', 'mips64el'] and
+      self.build_config.mips_arch_variant)
+
     # TODO(all): Combine "simulator" and "simulator_run".
     # TODO(machenbach): In GN we can derive simulator run from
     # target_arch != v8_target_arch in the dumped build config.
@@ -613,6 +617,7 @@ class BaseTestRunner(object):
       "gc_stress": False,
       "gcov_coverage": self.build_config.gcov_coverage,
       "isolates": options.isolates,
+      "mips_arch_variant": mips_arch_variant,
       "mode": self.mode_options.status_mode,
       "msan": self.build_config.msan,
       "no_harness": options.no_harness,