A number of small lfs_util.h QOL changes

- Changed the name of the LFS_CONFIG macro to LFS_UTIL to avoid
  confusion with the lfs_config struct. This also hints that LFS_UTIL
  is related to lfs_util.h.

  LFS_UTIL allows the user to override lfs_util.h so they can provide
  their own system-level dependencies such as malloc, tracing, builtins,
  stdint definitions, string.h, and others.

- Removed stdlib includes from lfs.h, these should all go through
  lfs_util.h to let users override these definitions if stdlib is
  unavailable on their system.

- Moved error code definitions to lfs_util.h. This lets users override
  the error codes to replace them with their own error codes and avoid
  a translation layer in some situations. Note the error codes must
  still be in the range of a negative int.

- Used proper stdint definitions in lfs_scmp.

bd/lfs_filebd.h

@@ -8,7 +8,6 @@
 #define LFS_FILEBD_H
 
 #include "lfs.h"
-#include "lfs_util.h"
 
 #ifdef __cplusplus
 extern "C"

bd/lfs_rambd.h

@@ -8,7 +8,6 @@
 #define LFS_RAMBD_H
 
 #include "lfs.h"
-#include "lfs_util.h"
 
 #ifdef __cplusplus
 extern "C"

bd/lfs_testbd.h

@@ -9,7 +9,6 @@
 #define LFS_TESTBD_H
 
 #include "lfs.h"
-#include "lfs_util.h"
 #include "bd/lfs_rambd.h"
 #include "bd/lfs_filebd.h"