The x86 MMU if full of code that returns 0 and 1 for retry/emulate.  Use
the existing RET_MMIO_PF_RETRY/RET_MMIO_PF_EMULATE enum, renaming it to
drop the MMIO part.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

CVE-2018-12207

(backported from commit 9b8ebbdb)
[tyhicks: Backport to 4.4
 - Some conditionals that checked for tracked pages did not exist due to
   the lack of commit 3d0c27ad ("KVM: MMU: let page fault handler be
   aware tracked page")
 - lower_32_bits(error_code) is not used in kvm_mmu_page_fault() due to
   the lack of commit 14727754 ("kvm: svm: Add support for
   additional SVM NPF error codes")]
Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>