shared: split out ioprio related stuff into ioprio-util.[ch]

No actual code changes, just some splitting out.

src/basic/ioprio-util.h

@@ -0,0 +1,18 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+#pragma once
+
+#include "macro.h"
+#include "missing_ioprio.h"
+
+int ioprio_class_to_string_alloc(int i, char **s);
+int ioprio_class_from_string(const char *s);
+
+static inline bool ioprio_class_is_valid(int i) {
+        return IN_SET(i, IOPRIO_CLASS_NONE, IOPRIO_CLASS_RT, IOPRIO_CLASS_BE, IOPRIO_CLASS_IDLE);
+}
+
+static inline bool ioprio_priority_is_valid(int i) {
+        return i >= 0 && i < IOPRIO_BE_NR;
+}
+
+int ioprio_parse_priority(const char *s, int *ret);