ARM: multi_v7_defconfig: enable ARM_ATAG_DTB_COMPAT

commit a0396b9bd5a4a7baf598b60d2ca53c605c440a42 upstream.

Without this, legacy platforms that can boot with a multiplatform
kernel but that need the DTB to be appended, won't have a way to pass
firmware-set bootargs to the kernel.

This is needed to boot multi_v7_defconfig on snowball, for instance.

Signed-off-by: Olof Johansson <olof@lixom.net>
Cc: Jason Cooper <jason@lakedaemon.net>
Cc: Kevin Hilman <khilman@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>