arm: mvebu: update defconfig with ATAG support when using DT

Some of the mvebu boards (mainly the development board) come with
plug-in RAM modules. This patch allows to let the bootloaders which
have no support for DTS to give the real amount of memory available on
the board.
Signed-off-by: NGregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: NJason Cooper <jason@lakedaemon.net>

arch/arm/configs/mvebu_defconfig

@@ -20,6 +20,7 @@ CONFIG_HIGHMEM=y
 CONFIG_ZBOOT_ROM_TEXT=0x0
 CONFIG_ZBOOT_ROM_BSS=0x0
 CONFIG_ARM_APPENDED_DTB=y
+CONFIG_ARM_ATAG_DTB_COMPAT=y
 CONFIG_VFP=y
 CONFIG_NET=y
 CONFIG_INET=y