aio / timers: Untangle include files

include/qemu/timer.h has no need to include main-loop.h and
doing so causes an issue for the next patch. Unfortunately
various files assume including timers.h will pull in main-loop.h.
Untangle this mess.

Signed-off-by: Alex Bligh <alex@alex.org.uk>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
diff --git a/hw/timer/sh_timer.c b/hw/timer/sh_timer.c
index 251a10d..07f0670 100644
--- a/hw/timer/sh_timer.c
+++ b/hw/timer/sh_timer.c
@@ -11,6 +11,7 @@
 #include "hw/hw.h"
 #include "hw/sh4/sh.h"
 #include "qemu/timer.h"
+#include "qemu/main-loop.h"
 #include "exec/address-spaces.h"
 #include "hw/ptimer.h"