package/openocd: require wchar for the xds110 driver

package/openocd: require wchar for the xds110 driver

The xds110 driver requires wchar, and is enabled by default. Make sure
to disable xds110 when wchar support is missing.

Fixes:
http://autobuild.buildroot.net/results/530bfe22ff509cf4ebfdf99a183312a1053f505f/
http://autobuild.buildroot.net/results/956538a0a6029137db19cce30dc340e2e30dd166/
http://autobuild.buildroot.net/results/ae7da2ce1389ece44a4ca65108fee02e318df7b3/

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>