KVM: Move and rename regs_modified

Touching the user space representation of KVM's VCPU state is -
naturally - a per-VCPU thing. So move the dirty flag into KVM_CPU_COMMON
and rename it at this chance to reflect its true meaning.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
diff --git a/cpu-defs.h b/cpu-defs.h
index 95068b5..7fdbe97 100644
--- a/cpu-defs.h
+++ b/cpu-defs.h
@@ -197,6 +197,7 @@
     const char *cpu_model_str;                                          \
     struct KVMState *kvm_state;                                         \
     struct kvm_run *kvm_run;                                            \
-    int kvm_fd;
+    int kvm_fd;                                                         \
+    int kvm_vcpu_dirty;
 
 #endif