efi_loader: allow creation of more device part nodes

Create device path nodes for UCLASS_ETH udevices.
Create device path nodes of block device children of UCLASS_MMC udevices.
Consistently use debug for unsupported nodes.
Set the log level to error.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
[agraf: Fix build failure by adding #ifdef CONFIG_DM_ETH]
Signed-off-by: Alexander Graf <agraf@suse.de>