[U-Boot] efi_loader: Allow bouncing for network

[Alexander Graf]

> So far bounce buffers were only used for disk I/O, but network I/O
> may suffer from the same problem.
> 
> On platforms that have problems doing DMA on high addresses, let's
> also bounce outgoing network packets. Incoming ones always already
> get bounced.
> 
> This patch fixes EFI PXE boot on ZynqMP for me.
> 
> Signed-off-by: Alexander Graf <agraf at suse.de>

Thanks, applied to