Set up idt and gdt

[MatiasVara]

See kvm_setup_gdt() at https://github.com/torvalds/linux/blob/c00c5e1d157bec0ef0b0b59aa5482eb8dc7e8e49/tools/testing/selftests/kvm/lib/x86_64/processor.c

[MatiasVara]

See also https://patchwork.kernel.org/project/kvm/patch/1532819412-51357-3-git-send-email-pbonzini@redhat.com/

[MatiasVara]

https://www.mail-archive.com/kvmarm@lists.cs.columbia.edu/msg33196.html