dlink-sge-image: add support for D-Link DIR-X1860 B1/DIR-X1550 A1

dlink-sge-image: add support for D-Link DIR-X1860 B1/DIR-X1550 A1

This adds the key and cert data used for DIR-X1860 B1 and DIR-X1550 A1
to support de-/encryption their firmware files.
Key and cert were extracted from the vendor gpl archive found here:
https://ftp.dlink.de/dir/dir-x1550/driver_software/DIR-X1550_sw_reva_GPLcode.tar.gz
and tested against vendor firmware for both revisions.
Note that images of DIR-X1860 revision A1 are not supported by this and
either use a different encryption method or different key/cert.

Signed-off-by: Christoph Krapp <[email protected]>
Link: https://github.com/openwrt/firmware-utils/pull/54
Signed-off-by: Hauke Mehrtens <[email protected]>