buildroot

system: move locale purging options to the "System configuration" menu

The options to purge locales and to generate locale data are currently
located in the toolchain menu. However, these options are not really
related to the toolchain per-se, they are more system-level
configuration options, much like the timezone selection option we
already have in the "System configuration" menu.

Therefore, it makes more sense to have the locale-related options in
the "System configuration" menu as well.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>