There is no real distinction between glevels=3 and glevels=4; both have
exactly the same format and the code is treated exactly the same way.  Drop
role.glevels and replace is with role.cr4_pae (which is meaningful).  This
simplifies the code a bit.

As a side effect, it allows sharing shadow page tables between pae and
longmode guest page tables at the same guest page.
Signed-off-by: NAvi Kivity <avi@redhat.com>
Signed-off-by: NMarcelo Tosatti <mtosatti@redhat.com>