haven: doorbell: Add IRQF_ONESHOT flag

Use the IRQF_ONESHOT flag while requesting the threaded interrupt.
This flag keeps the virtual interrupt line masked until the threaded
handler has executed.

Change-Id: I041823f8b30e4326d3b28635c80918e4b501432a
Signed-off-by: Chris Lew <clew@codeaurora.org>