hyperv_testdev: refactor for better maintainability

hyperv_testdev: refactor for better maintainability

Make hyperv_testdev slightly easier to follow and enhance in future.
For that, put the hyperv sint routes (wrapped in a helper structure) on
a linked list rather than a fixed-size array.  Besides, this way
HvSintRoute can be treated as an opaque structure, allowing for easier
refactoring of the core Hyper-V SynIC code in followup pathches.

Signed-off-by: Roman Kagan <rkagan@virtuozzo.com>
Message-Id: <20180921081836.29230-2-rkagan@virtuozzo.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>