hw/core: Move cpu.c, cpu.h from qom/ to hw/core/

Suggested-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20190709152053.16670-2-armbru@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
[Rebased onto merge commit 95a9457fd44; missed instances of qom/cpu.h
in comments replaced]

trace-events

@@ -129,7 +129,7 @@ vcpu guest_cpu_enter(void)
 # Targets: all
 vcpu guest_cpu_exit(void)
 
-# qom/cpu.c
+# hw/core/cpu.c
 
 # Reset the state of a virtual (guest) CPU
 #