spapr_iommu: Disable in-kernel IOMMU tables for >4GB windows

The existing KVM_CREATE_SPAPR_TCE ioctl only support 4G windows max as
the window size parameter to the kernel ioctl() is 32-bit so
there's no way of expressing a TCE window > 4GB.

We are going to add huge DMA windows support so this will create small
window and unexpectedly fail later.

This disables KVM_CREATE_SPAPR_TCE for windows bigger that 4GB.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Alexander Graf <agraf@suse.de>
