Rearrange block headers

Changing block.h or blockdev.h resulted in recompiling most objects.

Move DriveInfo typedef and BlockInterfaceType enum definitions
to qemu-common.h and rearrange blockdev.h use to decrease churn.

Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
diff --git a/hw/virtio-blk.c b/hw/virtio-blk.c
index 490cd41..c3a7343 100644
--- a/hw/virtio-blk.c
+++ b/hw/virtio-blk.c
@@ -13,6 +13,7 @@
 
 #include <qemu-common.h>
 #include "qemu-error.h"
+#include "blockdev.h"
 #include "virtio-blk.h"
 #ifdef __linux__
 # include <scsi/sg.h>