Gem5Device: Refactor into BaseGem5Device, Gem5LinuxDevice and Gem5AndroidDevice

- Refactored the Gem5Device to avoid duplicated code. There is now a
  BaseGem5Device which includes all of the shared functionality. The
  Gem5LinuxDevice and the Gem5AndroidDevice both inherit from
  BaseGem5Device, and LinuxDevice or AndroidDevice, respectively.

wlauto/common/gem5/__init__.py

@@ -0,0 +1,16 @@
+#    Copyright 2015 ARM Limited
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+