lantiq/xrx200: enable initramfs images

lantiq/xrx200: enable initramfs images

Commit eae6cac6a3 ("lantiq: add support for AVM FRITZ!Box 7362 SL"), but
one needs an initramfs image to flash OpenWrt from stock firmware (as
described in the commit log). This patch has the initramfs image built
by default.

Thanks to blogic (for pointing to the FEATURES declaration in the target
Makefiles) and Musashino on the forum for suggesting
config/Config-images.in needed editing too. While at it, reorder the
TARGET_INITRAMFS_COMPRESSION_LZMA declarations alphabetically.

This patch will result in initramfs images for all lantiq subtargets
that have the ramdisk flag set. I tested on the falcon and ase
subtargets, which lack that flag, to confirm they don't produce any
initramfs images with this patch - which they do not.

Given the limited scope of the lantiq (sub)target(s), blogic indicated
this should be OK.

Signed-off-by: Stijn Segers <foss@volatilesystems.org>
Signed-off-by: Petr Štetiar <ynezz@true.cz>
[fixed the wrong reference to eae6cac6a3 commit]