rockchip: puma-rk3399: defconfig: select PHY_MICREL_KSZ90X1

The RK3368-uQ7 uses a KSZ9031 PHY on-module.  Enable PHY_MICREL_KSZ90X1
in the associated defconfig (this somehow got lost with da3b9e7f).

References: da3b9e7f ("Move PHY_MICREL and PHY_MICREL_KSZ90X1 to Kconfig")
Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Acked-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>