bus: fsl-mc: don't assume an iommu is always present

There are certain scenarios where an iommu is not present, e.g.
booting in a VM. Let's support these scenarios by dropping the
check.

Signed-off-by: Laurentiu Tudor <laurentiu.tudor@nxp.com>
Link: https://lore.kernel.org/r/20200914105459.27448-1-laurentiu.tudor@nxp.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>