config/raspberrypi: rename our non-DT defconfig file

Since we no longer have a non-DT defconfig, and we no longer want to
advertise such a possibility (non-DT is being phased out), just rename
the DT-enabled defconfig file.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Floris Bos <bos@je-eigen-domein.nl>
Cc: Pascal de Bruijn <pmjdebruijn@pcode.nl>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>