iommu/pamu: Fix PAMU boot crash

Commit 68a17f0b introduced an initialization order
problem, where devices are linked against an iommu which is
not yet initialized. Fix it by initializing the iommu-device
before the iommu-ops are registered against the bus.

Reported-by: Michael Ellerman <mpe@ellerman.id.au>
Fixes: 68a17f0b ('iommu/pamu: Add support for generic iommu-device')
Signed-off-by: Joerg Roedel <jroedel@suse.de>