ARM: mvebu: enable Dove SoC in mvebu_v7_defconfig

ARM: mvebu: enable Dove SoC in mvebu_v7_defconfig

Since commit:

commit 6f3951aeca8bce2fe6d3868d75f61ff96a45b405
Author: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Date:   Thu Apr 24 22:58:30 2014 +0100

    ARM: 8042/1: iwmmxt: allow to build iWMMXt on Marvell PJ4B

fixed the error that prevented Dove SoC from being built with
the rest of the mvebu SoCs, we can now add it to the defconfig.

In addition, this commit enables SERIAL_OF_PLATFORM, which is required
to have UART on some of the boards.

Signed-off-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>