Add IOMMU_BUSWIDE ahci quirk.

Some controllers use PCI function 1 as the requester ID for DMA transfers,
but the controllers are not PCI multifunction.

Set the iommu buswide flag for them. This should instruct an IOMMU driver
to use the same translation rule for all the devices and functions of
a bus.

This was discovered on the ARM Neoverse N1 System Development Platform
(ARM N1SDP).

Bug reference: https://bugzilla.kernel.org/show_bug.cgi?id=42679

Reported by: andrew
Reviewed by: kib, mav
Sponsored by: Innovate DSbD
Differential Revision: https://reviews.freebsd.org/D26857