This commit switches to use the new gettext logic, which involves:
- using TARGET_NLS_DEPENDENCIES instead of hand-encoded dependencies
on gettext/host-gettext
- using TARGET_NLS_LIBS to force linking against libintl
- dropping BR2_PACKAGE_GETTEXT selection
- using BR2_SYSTEM_ENABLE_NLS instead of BR2_ENABLE_LOCALE to decide
if NLS support should be enabled or not
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>