Hyper-V: vmbus: implementat bus_get_dma_tag in vmbus

In ARM64 Hyper-V UFS filesystem is getting corruption and those
corruptions are consistently happening just after hitting a page
boundary. It is unable to correctly read disk blocks into buffers
that are not aligned to 512-byte boundaries.

It happens because storvsc needs physically contiguous memory which
may not be the case when bus_dma needs to create a bounce buffer.
This can happen when the destination is not cache-line aligned.

Hyper-V VMs have VMbus synthetic devices and PCI pass-thru devices
that are added dynamically via the VMbus protocol and are not
represented in the ACPI DSDT. Only the top level VMbus node exists
in the DSDT. As such, on ARM64 these devices don't pick up coherence
information and default to not hardware coherent.

PR: 267654, 272666
Reviewed by: andrew, whu
Tested by: lwhsu
MFC after: 3 days
Sponsored by: Microsoft
Differential Revision: https://reviews.freebsd.org/D41728