[PATCH] msi: only use a single irq_chip for msi interrupts

The logic works like this.

Since we no longer track the state logic by hand in msi.c startup and shutdown
are no longer needed.

By updating msi_set_mask_bit to work on msi devices that do not implement a
mask bit we can always call the mask/unmask functions.

What we really have are mask and unmask so we use them to implement the .mask
and .unmask functions instead of .enable and .disable.

By switching to the handle_edge_irq handler we only need an ack function that
moves the irq if necessary.  Which removes the old end and ack functions and
their peculiar logic of sometimes disabling an irq.

This removes the reliance on pre genirq irq handling methods.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Andi Kleen <ak@suse.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Greg KH <greg@kroah.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>