exec.h: fix coding style and change cpu_has_work to return bool

Before the next patch, fix coding style of the areas affected.

Change the type of the return value from cpu_has_work() and
qemu_cpu_has_work() to bool.

Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
diff --git a/cpu-all.h b/cpu-all.h
index 880f570..e839100 100644
--- a/cpu-all.h
+++ b/cpu-all.h
@@ -847,7 +847,7 @@
 
 void cpu_exit(CPUState *s);
 
-int qemu_cpu_has_work(CPUState *env);
+bool qemu_cpu_has_work(CPUState *env);
 
 /* Breakpoint/watchpoint flags */
 #define BP_MEM_READ           0x01