libelf: don't attempt to parse __xen_guest for PVH

libelf: don't attempt to parse __xen_guest for PVH

The legacy __xen_guest section doesn't support the PHYS32_ENTRY
elfnote, so it's pointless to attempt to parse the elfnotes from that
section when called from an hvm container.

Pass an hvm boolean parameter to the elf note parsing routine, so that
the respective parsing can be suppressed in case libelf is dealing with
an hvm container.

Suggested-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>