ARM: imx_v6_v7_defconfig: add CONFIG_MICREL_PHY

The driver for Micrel PHYs is required for the Apalis iMX6 module
plugged into a Ixora carrier board featuring an on-module Micrel
KSZ9031 Gigabit PHY.

Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>