ARM: multi_v5_defconfig: Enable support for MX21/MX27

Although the SoC support was already enabled, the drivers and machines
were missing.

Signed-off-by: Jan Luebbe <jlu@pengutronix.de>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>