kvm: x86: vmx: cleanup handle_ept_violation

Instead, just use PFERR_{FETCH, PRESENT, WRITE}_MASK
inside handle_ept_violation() for slightly better code.

Signed-off-by: Tiejun Chen <tiejun.chen@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>