xen/arm: iommu: Panic if not all IOMMUs are initialized

xen/arm: iommu: Panic if not all IOMMUs are initialized

At the moment, the platform can come up with only part of the IOMMUs
initialized. This could lead to a failure later on when building the
hardware domain or even trying to assign a device to a guest.

To avoid unwanted behavior, Xen will not continue if one of the IOMMUs
has not been initialized correctly.

[stefano: fix typo in comment, add '\n' to panic message]

Signed-off-by: Julien Grall <julien.grall@arm.com>
Signed-off-by: Stefano Stabellini <stefano.stabellini@xilinx.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Tested-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>