cutils: Move size_to_str() from "qemu-common.h" to "qemu/cutils.h"

cutils: Move size_to_str() from "qemu-common.h" to "qemu/cutils.h"

"qemu/cutils.h" contains various qemu_strtosz_*() functions
useful to convert strings to size. It seems natural to have
the opposite usage (from size to string) there too.

The function definition is already in util/cutils.c.

Signed-off-by: Philippe Mathieu-Daudé <[email protected]>
Reviewed-by: John Snow <[email protected]>
Reviewed-by: Peter Xu <[email protected]>
Message-Id: <20190903120555[email protected]>
Signed-off-by: Laurent Vivier <[email protected]>