Disable legacy codepage handling in bootloaders

Turn off legacy codepage handling in the filesystem code for
bootloaders, and support ISO-8859-1 (Latin-1) only.

This only affects DOS 8.3 filename parsing when FAT32 long
names are unavailable; long names are Unicode and can always
be decoded properly regardless of this setting.

In reality, bootloaders never supported codepages other than
Latin-1 in the first place. They did contain the code to load
codepages from disk, but had no way to actually change the
codepage away from Latin-1.

Compiling out this useless codepage handling code frees up
precious space for very size-constrained bootloaders like the
Sansa e200v2.

Change-Id: I26b049dd648fed4a0cc61fa938faa84e9816ab7d

firmware/common/file_internal.c

@@ -223,6 +223,7 @@ int test_dir_empty_internal(struct filestr_base *stream)
 /* iso decode the name to UTF-8 */
 void iso_decode_d_name(char *d_name)
 {
+#ifdef HAVE_FILESYSTEM_CODEPAGE
     if (is_dotdir_name(d_name))
         return;
 
@@ -232,6 +233,9 @@ void iso_decode_d_name(char *d_name)
     /* This MUST be the default codepage thus not something that could be
        loaded on call */
     iso_decode(shortname, d_name, -1, len + 1);
+#else
+    (void)d_name;
+#endif
 }
 
 #ifdef HAVE_DIRCACHE