android: configs: Initial commit of Android config fragments

- Add 2 files that contain the minimal and recommended kernel config
options respectively.
- Add a README to explain their purpose and how to use them to
generate a device config compatible with Android.

Change-Id: I3a4883f3b04d2820e90ceb3c4d02390d6458d6ce
Signed-off-by: Rom Lemarchand <romlem@google.com>