evtchn: print ABI specific state with the 'e' debug key

evtchn: print ABI specific state with the 'e' debug key

In the output of the 'e' debug key, print some ABI specific state in
addition to the (p)ending and (m)asked bits.

For the 2-level ABI, print the state of that event's selector
bit. e.g.,

(XEN)     port [p/m/s]
(XEN)        1 [0/0/1]: s=3 n=0 x=0 d=0 p=74
(XEN)        2 [0/0/1]: s=3 n=0 x=0 d=0 p=75

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Keir Fraser <keir@xen.org>