ARM: omap2plus_defconfig: Enable support for micrell phys

The phyCORE-AM335x SoM with PCM-953 carrierboard has a
KSZ9021 phy mounted. To add support for this we need to enable
the micrell phy driver in the config.

Signed-off-by: Teresa Remmet <t.remmet@phytec.de>
Signed-off-by: Tony Lindgren <tony@atomide.com>