support/kconfig: fix compiler warnings

Compiling on Ubuntu 20.04 generates this:

./util.c: In function ‘file_write_dep’
./util.c:54:18: warning: ‘..config.tmp’ directive writing 12 bytes into a region of size between 1 and 4097 [-Wformat-overflow=]
   54 |  sprintf(buf, "%s..config.tmp", dir);
      |                  ^~~~~~~~~~~~
./util.c:54:2: note: ‘sprintf’ output between 13 and 4109 bytes into a destination of size 4097
   54 |  sprintf(buf, "%s..config.tmp", dir);
      |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

and similar warnings on confdata.c, lines 778, 989, 995, 1000, 1007,
1040, 1046 and 1054. Avoid the warnings by enlarging the destination
buffer of fprintf().

Normally, we want changes to kconfig to be reflected by patches in
support/kconfig/patches. This makes it easier to resync with upstream
kconfig. However, in this case, everything that is changed here is
already changed completely (and differently) upstream, so there is no
added value in keeping the patch.

Signed-off-by: Edgar Bonet <bonet@grenoble.cnrs.fr>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>