KVM: MMU: change direct_page_fault() arguments to kvm_page_fault

Add fields to struct kvm_page_fault corresponding to
the arguments of direct_page_fault().  The fields are
initialized in the callers, and direct_page_fault()
receives a struct kvm_page_fault instead of having to
extract the arguments out of it.

Also adjust FNAME(page_fault) to store the max_level in
struct kvm_page_fault, to keep it similar to the direct
map path.

Suggested-by: Isaku Yamahata <isaku.yamahata@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>