iommm/amd: Store irq domain in struct device

As the next step to make X86 utilize the direct MSI irq domain operations
store the irq domain pointer in the device struct when a device is probed.

It only overrides the irqdomain of devices which are handled by a regular
PCI/MSI irq domain which protects PCI devices behind special busses like
VMD which have their own irq domain.

No functional change.

It just avoids the redirection through arch_*_msi_irqs() and allows the
PCI/MSI core to directly invoke the irq domain alloc/free functions instead
of having to look up the irq domain for every single MSI interupt.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Joerg Roedel <jroedel@suse.de>
Link: https://lore.kernel.org/r/20200826112333.806328762@linutronix.de