toolchain-crosstool-ng: use the Crosstool-ng config options instead of the common hidden ones

Since we are some day going to finally rename the badly named common
toolchain options (BR2_USE_WCHAR, BR2_ENABLE_LOCALE, BR2_INET_RPC,
etc.) into something more logical, let's start using the Crosstool-NG
toolchain options in the Crosstool-NG code.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Reviewed-by: Yann E. MORIN <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>