KVM: MMU: Expose the LA57 feature to VM.

KVM: MMU: Expose the LA57 feature to VM.

This patch exposes 5 level page table feature to the VM.
At the same time, the canonical virtual address checking is
extended to support both 48-bits and 57-bits address width.

Signed-off-by: Yu Zhang <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>