staging: mei: enable msi when supported

enable msi when supported
also in that case we can drop the quick handler
from the threaded interrupt that protected us from
handling USB interrupts

Signed-off-by: Maarten Lankhorst <m.b.lankhorst@gmail.com>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>