PPC: install mpc8544ds.dtb

We don't install mpc8544ds.dtb, which means that -M mpc8544ds doesn't
work when installed. Fix it by installing the file.
Signed-off-by: NAlexander Graf <agraf@suse.de>

Makefile

@@ -185,6 +185,7 @@ ppc_rom.bin openbios-sparc32 openbios-sparc64 openbios-ppc \
 pxe-e1000.rom pxe-eepro100.rom pxe-ne2k_pci.rom \
 pxe-pcnet.rom pxe-rtl8139.rom pxe-virtio.rom \
 bamboo.dtb petalogix-s3adsp1800.dtb petalogix-ml605.dtb \
+mpc8544ds.dtb \
 multiboot.bin linuxboot.bin \
 s390-zipl.rom \
 spapr-rtas.bin slof.bin