kernel: Use the debian infrastructure to construct kernel config files

kernel: Use the debian infrastructure to construct kernel config files

This is the first step towards abandonding make-kpkg. The next
step is to remove the kernel config files under
$(KERNEL_DIR)/files/Config, thereby requiring the use
of config files in $(KERNEL_DIR)/files/debian.chrome/config

Signed-off-by: Tim Gardner <tim.gardner@canonical.com>;