KVM: SVM: limit kvm_handle_page_fault to #PF handling

It has always annoyed me a bit how SVM_EXIT_NPF is handled by
pf_interception.  This is also the only reason behind the
under-documented need_unprotect argument to kvm_handle_page_fault.
Let NPF go straight to kvm_mmu_page_fault, just like VMX
does in handle_ept_violation and handle_ept_misconfig.

Reviewed-by: Brijesh Singh <brijesh.singh@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>