KVM: x86 emulator: add new ->halt() callback

Instead of reaching into vcpu internals.

Signed-off-by: Avi Kivity <avi@redhat.com>

diff --cc arch/x86/include/asm/kvm_emulate.h
Simple merge

diff --cc arch/x86/kvm/emulate.c
Simple merge

diff --cc arch/x86/kvm/x86.c
Simple merge