Originally libv4l2_codec2_common is small library that only contains
some constant definitions, so it's efficient to link it as static
library. Now the library becomes larger. This CL changes to link it as
shared library to prevent duplicating the content into its dependency
libraries and binaries.

Bug: 160110407
Test: mmm external/v4l2_codec2

Change-Id: Ie0c08bdd694d7226ce430af9148e0c8919126c79