KVM: arm64: nv: Inject SEA if kvm_translate_vncr() can't resolve PFN

In the Linux kernel, the following vulnerability has been resolved: KVM: arm64: nv: Inject SEA if kvm_translate_vncr() can't resolve PFN kvm_handle_vncr_abort() assumes that s1_walk_result conveys an abort when kvm_translate_vncr() returns -EFAULT. This is not always the case as it's possible to encounter 'late' failures on the output of S1 translation, e.g. a GFN outside of the memslots. Fix it by preparing an external abort before returning from kvm_translate_vncr(). Get rid of the BUG_ON() in the fault injection path while at it.