hyperv/vmbus: Avoid unnecessary mb()

Sponsored by:   Microsoft
Differential Revision:  https://reviews.freebsd.org/D7333

hyperv/vmbus: Inclusion cleanup

Sponsored by:   Microsoft
Differential Revision:  https://reviews.freebsd.org/D7334

hyperv/vmbus: Reindent function declarations.

Sponsored by:   Microsoft
Differential Revision:  https://reviews.freebsd.org/D7344

hyperv/vmbus: Forward declare static functions

Sponsored by:   Microsoft
Differential Revision:  https://reviews.freebsd.org/D7346

hyperv/vmbus: Move driver glue to the beginning of the files

Just as most of other drivers do.  And move sysinit function close
to its SYSINIT.

Sponsored by:   Microsoft
Differential Revision:  https://reviews.freebsd.org/D7347

hyperv/vmbus: Revoke unnecessary exposure of vmbus softc

Sponsored by:   Microsoft
Differential Revision:  https://reviews.freebsd.org/D7348