lib: fs: add library for implementing a filesystem service

lib/libfs/superblock.c

@@ -0,0 +1,11 @@
+#include <fs/superblock.h>
+#include <stddef.h>
+
+struct fs_inode *fs_superblock_alloc_inode(struct fs_superblock *sb)
+{
+	if (!sb->s_ops->s_alloc_inode) {
+		return NULL;
+	}
+
+	return sb->s_ops->s_alloc_inode(sb);
+}