"ARM: shmobile: marzen: Switch to DT_MACHINE_START" moves marzen
over to use DT_MACHINE_START, however, the prevalent boot loader
does not support booting with a separate dtb. Thus, it makes
sense to use ARM_APPENDED_DTB by default.

This is consistent with other shmobile defconfigs.
Acked-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>