kbuild: turn on -Wrestrict by default

All known -Wrestrict warnings are addressed now, so don't disable the
warning any more.

Link: https://lkml.kernel.org/r/20240415122037.1983124-4-arnd@kernel.org
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Kees Cook <keescook@chromium.org>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nicolas Schier <nicolas@fjasle.eu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>