tools/headers: prevent adding two __align8__ to uint64_t in ARM headers

tools/headers: prevent adding two __align8__ to uint64_t in ARM headers

Due to the fact that on ARM headers types are substituted to uint64_t and
then uint64_t is also substituted to contain the aligment, this would lead
to some types containing two __align8__ directives. Fix this by first
expanding Xen specific types to uint64_t only, and then replacing all the
uint64_t types to __align8__ uint64_t. This relies on the fact that all
Xen-specific types will have longer names, so they will always be replaced
first.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: Doug Goldstein <cardoe@cardoe.com>
Release-acked-by: Wei Liu <wei.liu2@citrix.com>