raspberrypi-cm3.conf: drop KBUILD_DEFCONFIG definition
raspberrypi-cm3.conf: drop KBUILD_DEFCONFIG definition

KBUILD_DEFCONFIG should be defined by the kernel recipe instead, such as
linux-raspberrypi.

Signed-off-by: Ricardo Salveti <d4e7430f1534a12df46cedd1ac369935436dbb94@foundries.io>

agherzan/meta-raspberrypi,schnitzeltony/meta-raspberrypi,schnitzeltony/meta-raspberrypi,agherzan/meta-raspberrypi,agherzan/meta-raspberrypi,agherzan/meta-raspberrypi,schnitzeltony/meta-raspberrypi,agherzan/meta-raspberrypi,agherzan/meta-raspberrypi