Adds default (mock) Context Hub HAL 1.2 impl

Also refactors common code.

Bug: 166845383
Test: Compile only (VTS test coming up in future CL)
Change-Id: Iae6cf09e2fffb854af61c29e6004ceb062a892b3
diff --git a/contexthub/1.2/default/android.hardware.contexthub@1.2.xml b/contexthub/1.2/default/android.hardware.contexthub@1.2.xml
new file mode 100644
index 0000000..ec6c684
--- /dev/null
+++ b/contexthub/1.2/default/android.hardware.contexthub@1.2.xml
@@ -0,0 +1,11 @@
+<manifest version="1.0" type="device">
+    <hal format="hidl">
+        <name>android.hardware.contexthub</name>
+        <transport>hwbinder</transport>
+        <version>1.2</version>
+        <interface>
+            <name>IContexthub</name>
+            <instance>default</instance>
+        </interface>
+    </hal>
+</manifest>