x86/p2m: allocate logdirty_ranges for altp2ms

x86/p2m: allocate logdirty_ranges for altp2ms

For now, only do allocation/deallocation; keeping them in sync
will be done in subsequent patches.

Logdirty synchronization will only be done for active altp2ms;
so allocate logdirty rangesets (copying the host logdirty
rangeset) when an altp2m is activated, and free it when
deactivated.

Signed-off-by: Razvan Cojocaru <rcojocaru@bitdefender.com>
Tested-by: Tamas K Lengyel <tamas@tklengyel.com>
Reviewed-by: George Dunlap <george.dunlap@citrix.com>