CRIS: proper defconfig setup

This patch moves the cris defconfigs to arch/cris/configs/ where they
belong.

As a side effect they can now be used directly through e.g.
  make ARCH=cris artpec_3_defconfig

The default defconfig is set through KBUILD_DEFCONFIG.

Signed-off-by: Adrian Bunk <adrian.bunk@movial.fi>
Signed-off-by: Jesper Nilsson <jesper.nilsson@axis.com>