Add V4L2 Control Factory

Also moves all control factory methods into a separate file.

BUG: 30900438
TEST: unit tests pass
Change-Id: I885903d8e23a548b63fd20006568145a233c0316
diff --git a/modules/camera/3_4/Android.mk b/modules/camera/3_4/Android.mk
index 1e7f4d6..ae28598 100644
--- a/modules/camera/3_4/Android.mk
+++ b/modules/camera/3_4/Android.mk
@@ -50,6 +50,7 @@
   v4l2_wrapper.cpp \
 
 v4l2_test_files := \
+  metadata/control_factory_test.cpp \
   metadata/control_test.cpp \
   metadata/enum_converter_test.cpp \
   metadata/ignored_control_delegate_test.cpp \