cpus: Pass CPUState to qemu_cpu_is_self()

Change return type to bool, move to include/qemu/cpu.h and
add documentation.

Signed-off-by: Andreas Färber <afaerber@suse.de>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
[AF: Updated new caller qemu_in_vcpu_thread()]
diff --git a/exec.c b/exec.c
index b0ed593..a85a9b1 100644
--- a/exec.c
+++ b/exec.c
@@ -1693,6 +1693,7 @@
 /* mask must never be zero, except for A20 change call */
 static void tcg_handle_interrupt(CPUArchState *env, int mask)
 {
+    CPUState *cpu = ENV_GET_CPU(env);
     int old_mask;
 
     old_mask = env->interrupt_request;
@@ -1702,7 +1703,7 @@
      * If called from iothread context, wake the target cpu in
      * case its halted.
      */
-    if (!qemu_cpu_is_self(env)) {
+    if (!qemu_cpu_is_self(cpu)) {
         qemu_cpu_kick(env);
         return;
     }