include: Move qemu_madvise() and related #defines to new qemu/madvise.h

The function qemu_madvise() and the QEMU_MADV_* constants associated
with it are used in only 10 files.  Move them out of osdep.h to a new
qemu/madvise.h header that is included where it is needed.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20220208200856.3558249-2-peter.maydell@linaro.org
diff --git a/backends/hostmem.c b/backends/hostmem.c
index 4c05862..b2a5e90 100644
--- a/backends/hostmem.c
+++ b/backends/hostmem.c
@@ -19,6 +19,7 @@
 #include "qemu/config-file.h"
 #include "qom/object_interfaces.h"
 #include "qemu/mmap-alloc.h"
+#include "qemu/madvise.h"
 
 #ifdef CONFIG_NUMA
 #include <numaif.h>