Rather than relying on the X86XSaveArea structure definition directly,
the routines that manipulate the XSAVE state area should observe the
offsets declared in the x86_ext_save_areas array.

Currently the offsets declared in the array are derived from the
structure definition, resulting in no functional change.

Signed-off-by: David Edmondson <david.edmondson@oracle.com>
Message-Id: <20210705104632.2902400-7-david.edmondson@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>