package/freerdp: needs wchar

Also add reverse dependency for Weston.

Fix build error:
make[3]: Entering directory '/home/tetsuya/buildroot/br/output/build/freerdp-b21ff842ef3de5837513042dc30488b12bd9cf9d'
In file included from /home/tetsuya/buildroot/br/output/build/freerdp-b21ff842ef3de5837513042dc30488b12bd9cf9d/winpr/include/winpr/winsock.h:24:0,
                 from /home/tetsuya/buildroot/br/output/build/freerdp-b21ff842ef3de5837513042dc30488b12bd9cf9d/winpr/libwinpr/winsock/winsock.c:24:
/home/tetsuya/buildroot/br/output/build/freerdp-b21ff842ef3de5837513042dc30488b12bd9cf9d/winpr/include/winpr/wtypes.h:132:1: error: unknown type name ‘wchar_t’
 typedef wchar_t UNICODE;

Signed-off-by: Fabio Porcedda <fabio.porcedda@gmail.com>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>