kvm: x86: add tsc_offset field to struct kvm_vcpu_arch

A future commit will want to easily read a vCPU's TSC offset,
so we store it in struct kvm_arch_vcpu_arch for easy access.

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index cd82bf7..ddffcfb 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -568,6 +568,7 @@
 		struct kvm_steal_time steal;
 	} st;
 
+	u64 tsc_offset;
 	u64 last_guest_tsc;
 	u64 last_host_tsc;
 	u64 tsc_offset_adjustment;