gcm_driver: Move GN build file into common directory.

This is in spirit with gn philosophy.

Tested on Linux with the following command line:
$ gn gen out-gn/Release --args='is_debug=false is_component_build=false symbol_level=1'

BUG=None
TEST=see above
[email protected],[email protected]

Review URL: https://codereview.chromium.org/1246653004

Cr-Commit-Position: refs/heads/master@{#339902}
4 files changed