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/qemu-coroutine-io.c b/qemu-coroutine-io.c
index c4df35a..054ca70 100644
--- a/qemu-coroutine-io.c
+++ b/qemu-coroutine-io.c
@@ -26,6 +26,7 @@
 #include "qemu/sockets.h"
 #include "block/coroutine.h"
 #include "qemu/iov.h"
+#include "qemu/main-loop.h"
 
 ssize_t coroutine_fn
 qemu_co_sendv_recvv(int sockfd, struct iovec *iov, unsigned iov_cnt,