modpost: Enable section warning from *driver to .exit.text

There used to be several offenders, but now that for all of them patches
were sent and most of them were applied, enable the warning also for
builds without W=1.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>