MFC 318136

MFC 318136

    hyperv/vmbus: Reorganize vmbus device tree

    For GEN1 Hyper-V, vmbus is attached to pcib0, which contains the
    resources for PCI passthrough and SR-IOV.  There is no
    acpi_syscontainer0 on GEN1 Hyper-V.

    For GEN2 Hyper-V, vmbus is attached to acpi_syscontainer0, which
    contains the resources for PCI passthrough and SR-IOV.  There is
    no pcib0 on GEN2 Hyper-V.

    The ACPI VMBUS device now only holds its _CRS, which is empty as
    of this commit; its existence is mainly for upward compatibility.

    Device tree structure is suggested by jhb@.

    Tested-by:	dexuan@
    Collabrated-wth:	dexuan@
    Sponsored by:	Microsoft
    Differential Revision:	https://reviews.freebsd.org/D10565