config: Adjust Phytec imx8mm module config to support NVME disk

This change adds support for PCIe connected nvme disk - phyBOARD-Polis
base board.

One needs to call following commands in u-boot:
> pci enum
> nvme scan
> nvme info

And then ones to access proper file system (like fat[ls|load|write],
ext4[ls|load|write]).

Signed-off-by: Lukasz Majewski <lukma@denx.de>