x86/EPT: don't walk entire page tables when globally changing types

x86/EPT: don't walk entire page tables when globally changing types

Instead leverage the EPT_MISCONFIG VM exit by marking just the top
level entries as needing recalculation of their type, propagating the
the recalculation state down as necessary such that the actual
recalculation gets done upon access.

For this to work, we have to
- restrict the types between which conversions can be done (right now
  only the two types involved in log dirty tracking need to be taken
  care of)
- remember the ranges that log dirty tracking was requested for as well
  as whether global log dirty tracking is in effect

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Tim Deegan <tim@xen.org>