Change TARGET_ROOTFS_PARTSIZE from 128 to 104 MiB, so the whole image
(bootloader + boot + root) will fit on a 128MB CF card by default.
With these settings, the generated images (tested on x86-generic and
x86-64) have 126,353,408 bytes; the smallest CF card marketed as "128MB"
that I found a datasheet for (a Transcend TS128MCF80) has 126,959,616
bytes.
Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>