unicode: add MODULE_DESCRIPTION() macros

Currently 'make W=1' reports:
WARNING: modpost: missing MODULE_DESCRIPTION() in fs/unicode/utf8data.o
WARNING: modpost: missing MODULE_DESCRIPTION() in fs/unicode/utf8-selftest.o

Add a MODULE_DESCRIPTION() to utf8-selftest.c and utf8data.c_shipped,
and update mkutf8data.c to add a MODULE_DESCRIPTION() to any future
generated utf8data file.

Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Link: https://lore.kernel.org/r/20240524-md-unicode-v1-1-e2727ce8574d@quicinc.com


Signed-off-by: Gabriel Krisman Bertazi <krisman@suse.de>