PCI/MSI: Drop use of msi_controller from core code

As there is no driver using msi_controller, we can now safely
remove its use from the PCI probe code.

Link: https://lore.kernel.org/r/20210330151145.997953-8-maz@kernel.org


Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>