Hypercall based pte updates are faster than faults, and also allow use
of the lazy MMU mode to batch operations.

Don't report the feature if two dimensional paging is enabled.

[avi:
 - guest/host split
 - fix 32-bit truncation issues
 - adjust to mmu_op
 - adjust to ->release_*() renamed
 - add ->release_pud()]
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>