This patch introduces the framework required for architectures to supply
several independent configurations. Three architectures does this today:
ppc, ppc64 and arm.
The infrastructure provided here requires the files to be located in
the following directory:
arch/$(ARCH)/configs
The file shall be named <board>_defconfig

To select the configuration for ppc/gemini simply issue the following command:
make gemini_defconfig
This will generate a valid configuration.

ppc and ppc64 already comply to the above requirements, arm needs some
trivial updates.