drm/nouveau/pci: do a msi rearm on init

On my GP107 when I load nouveau after unloading it, for some reason the
GPU stopped sending or the CPU stopped receiving interrupts if MSI was
enabled.

Doing a rearm once before getting any interrupts fixes this.

Signed-off-by: Karol Herbst <kherbst@redhat.com>
Reviewed-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>