[U-Boot] efi_loader: Allocate memory handle for mem dp

[Alexander Graf]

> When we boot using memdp (bootefi on an address without previous
> load that populates the device path) then the memory device path
> we pass in is not backed by any handle.
> 
> That can result in weird effects. For example grub gets very grumpy
> about this inside the efi_net module and just loops endlessly.
> 
> So let's expose a simple handle that the memory device path is backed
> on. That way any code that looks for the device the dp is on, finds
> one.
> 
> Signed-off-by: Alexander Graf <agraf at suse.de>

Thanks, applied to efi-next

Alex