VFIO: platform: clear IRQ_NOAUTOEN when de-assigning the IRQ

The vfio platform driver currently sets the IRQ_NOAUTOEN before
doing the request_irq to properly handle the user masking. However
it does not clear it when de-assigning the IRQ. This brings issues
when loading the native driver again which may not explicitly enable
the IRQ. This problem was observed with xgbe driver.

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