Move Android.mks to their parent dir.

So we don't need "../" to reference source files in the common/
directory.
"../" in LOCAL_SRC_FILES causes build race condition: the path of object
file of ../common/src/extra_data_handler.cpp in vdec actually is the same
as the path of object file of ../common/src/extra_data_handler.cpp in
venc.

Bug: 12779537
Change-Id: Ifd7fef36810c15fbe7854aeb3d505fba63f5d7e2