Everywhere: Add serenity_dev_{makedev,major,minor}

Add them in `<Kernel/API/Device.h>` and use these to provides
`{makedev,major,minor}` in `<sys/sysmacros.h>`. It aims to be more in
line with other Unix implementations and avoid code duplication in user
land.

Userland/Utilities/mknod.cpp

@@ -8,13 +8,9 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <sys/stat.h>
+#include <sys/sysmacros.h>
 #include <unistd.h>
 
-constexpr unsigned encoded_device(unsigned major, unsigned minor)
-{
-    return (minor & 0xff) | (major << 8) | ((minor & ~0xff) << 12);
-}
-
 static int usage()
 {
     warnln("usage: mknod <name> <c|b|p> [<major> <minor>]");
@@ -63,7 +59,7 @@ int main(int argc, char** argv)
         minor = atoi(argv[4]);
     }
 
-    int rc = mknod(name, mode, encoded_device(major, minor));
+    int rc = mknod(name, mode, makedev(major, minor));
     if (rc < 0) {
         perror("mknod");
         return 1;