xen/xsm: Add xsm_default parameter to XSM hooks

xen/xsm: Add xsm_default parameter to XSM hooks

Include the default XSM hook action as the first argument of the hook
to facilitate quick understanding of how the call site is expected to
be used (dom0-only, arbitrary guest, or device model). This argument
does not solely define how a given hook is interpreted, since any
changes to the hook's default action need to be made identically to
all callers of a hook (if there are multiple callers; most hooks only
have one), and may also require changing the arguments of the hook.

Signed-off-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
Acked-by: Tim Deegan <tim@xen.org>
Committed-by: Keir Fraser <keir@xen.org>