IO-APIC: Reformat IO-APIC RTE debug info (v2)

IO-APIC: Reformat IO-APIC RTE debug info (v2)

Having the columns aligned makes for much easier reading.  Also remove
the commas which only add to visual clutter in combination with
spaces.

Furthermore, printing fewer characters makes it less likely that the
serial buffer will overflow resulting in loss of critical debugging
information.

Changes since v1:
 *  Format vector as hex rather than dec
 *  Contract some names
 *  destination mode uses 'L' or 'P' instead of full words
 *  trigger mode uses 'L' or 'E' instead of full words
 *  delivery mode uses short string instead of a number

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Committed-by: Keir Fraser <keir@xen.org>