Use KConfig for /cfg filesystem size

Because clearfog and Epia have vastly differing flash sizes, we will
have to specify the desired size of the /cfg filesystem template that we
are making. Let's convert this to a "package" so that we have easy
access to the Kconfig tools -- even though it really isn't about any
"package" per se. On a flip side, this should allow for proper
parallelization of image building, yay!

Change-Id: Ic95a201ab7874711514bdc8b2e60b711db97ddc0
diff --git a/configs/czechlight_clearfog_defconfig b/configs/czechlight_clearfog_defconfig
index eeb4687..bbe9ae7 100644
--- a/configs/czechlight_clearfog_defconfig
+++ b/configs/czechlight_clearfog_defconfig
@@ -12,7 +12,7 @@
 BR2_TARGET_GENERIC_GETTY_BAUDRATE_115200=y
 # BR2_TARGET_GENERIC_REMOUNT_ROOTFS_RW is not set
 BR2_ROOTFS_OVERLAY="$(BR2_EXTERNAL_CZECHLIGHT_PATH)/board/czechlight/common/overlay/ $(BR2_EXTERNAL_CZECHLIGHT_PATH)/board/czechlight/clearfog/overlay/"
-BR2_ROOTFS_POST_BUILD_SCRIPT="$(BR2_EXTERNAL_CZECHLIGHT_PATH)/board/czechlight/common/mk-empty-cfg-fs.sh $(BR2_EXTERNAL_CZECHLIGHT_PATH)/board/czechlight/common/install-rauc-cert.sh $(BR2_EXTERNAL_CZECHLIGHT_PATH)/board/czechlight/clearfog/copy-boot-scr.sh"
+BR2_ROOTFS_POST_BUILD_SCRIPT="$(BR2_EXTERNAL_CZECHLIGHT_PATH)/board/czechlight/common/install-rauc-cert.sh $(BR2_EXTERNAL_CZECHLIGHT_PATH)/board/czechlight/clearfog/copy-boot-scr.sh"
 BR2_ROOTFS_POST_IMAGE_SCRIPT="support/scripts/genimage.sh $(BR2_EXTERNAL_CZECHLIGHT_PATH)/board/czechlight/clearfog/mk-rauc-bundle.sh ${BR2_EXTERNAL_CZECHLIGHT_PATH}/board/czechlight/clearfog/usb-flash-genimage.sh"
 BR2_ROOTFS_POST_SCRIPT_ARGS="-c $(BR2_EXTERNAL_CZECHLIGHT_PATH)/board/czechlight/clearfog/genimage.cfg"
 BR2_LINUX_KERNEL=y
@@ -68,4 +68,6 @@
 BR2_PACKAGE_HOST_GENIMAGE=y
 BR2_PACKAGE_HOST_MTOOLS=y
 BR2_PACKAGE_HOST_RAUC=y
+BR2_PACKAGE_CZECHLIGHT_CFG_FS=y
+CZECHLIGHT_CFG_FS_SIZE="256M"
 CZECHLIGHT_NETCONF=y