hw/vfio/platform: do not set resamplefd for edge-sensitive IRQS

In irqfd mode, current code attempts to set a resamplefd whatever
the type of the IRQ. For an edge-sensitive IRQ this attempt fails
and as a consequence, the whole irqfd setup fails and we fall back
to the slow mode. This patch bypasses the resamplefd setting for
non level-sentive IRQs.

Signed-off-by: Eric Auger <eric.auger@linaro.org>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
