package/x11r7/xdriver_xf86-video-fbturbo: needs dri2 for libump

xdriver_xf86-video-fbturbo has an optional dependency to libump
currently not handled by buildroot:
https://github.com/ssvb/xf86-video-fbturbo/blob/master/configure.ac#L91

If libump was compiled incidentally before xdriver_xf86-video-fbturbo
sunxi_mali_ump_dri2.c is compiled which depends on dri2:
https://github.com/ssvb/xf86-video-fbturbo/blob/master/src/Makefile.am#L59

This patch adds a dependency for dri2proto to enable dri2 support in
X.org and adds libump as dependency for a reproducable build to fix
http://autobuild.buildroot.net/results/656/656520682a5ac6fe5e1e741e1a92b1eab4245f2d/



[Peter: also add dri2proto to _DEPENDENCIES]
Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>