xsm/xen_version: Add XSM for most of xen_version hypercall

xsm/xen_version: Add XSM for most of xen_version hypercall

Most of XENVER_* have now an XSM check for their sub-ops.

The subop for XENVER_commandline is now a priviliged operation.
To not break guests we still return an string - but it is
just '<denied>\0'.

The XENVER_[version|platform_parameters|get_features] - will
always return an value to the guest.

The rest: XENVER_[extraversion|capabilities|page_size|
guest_handle|changeset| compile_info] behave as before -
allowed by default for all guests if using the XSM default
policy or with the dummy one. And if the system admin
wants to curtail access to some of them - they can do
that now with a non-default XSM policy.

Also we add a local variable block.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
---
Cc: Daniel De Graaf <dgdegra@tycho.nsa.gov>
Cc: Ian Jackson <ian.jackson@eu.citrix.com>
Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Cc: Wei Liu <wei.liu2@citrix.com>
v2: Do XSM check for all the XENVER_ ops.
 - Add empty data conditions.
 - Return <denied> for priv subops.
 - Move extraversion from priv to normal. Drop the XSM check
    for the non-priv subops.
v3:
 - Add +1 for strlen(xen_deny()) to include NULL. Move changeset,
    compile_info to non-priv subops.
 - Remove the \0 on xen_deny()
 - Add new XSM domain for xenver hypercall. Add all subops to it.
 - Remove the extra line, Add Ack from Daniel
v4:
 - Rename the XSM from xen_version_op to xsm_xen_version.
   Prefix the types with 'xen' to distinguish it from another
   hypercall performing similar operation. Removed Ack from Daniel
   as it was so large. Add local variable block.
v5:
 - Make XENVER_platform_parameters,get_features,version be excluded
   from the XSM check per Jans' review. Add BUILD_BUG_CHECK and fix
   odd line removals. Remove stray changes and fix spelling.