tools: Move ARRAY_SIZE() into xen-tools/libs.h

tools: Move ARRAY_SIZE() into xen-tools/libs.h

xen-tools/libs.h currently contains a shared BUILD_BUG_ON() implementation and
is used by some tools.  Extend this to include ARRAY_SIZE and clean up all the
opencoding.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
(cherry picked from commit e1b7eb92d3ec6ce3ca68cffb36a148eb59f59613)

Gbp-Pq: Name 0024-tools-Move-ARRAY_SIZE-into-xen-tools-libs.h.patch