opengl: libgles and libegl also provided by gpu-viv-bin-mx6q

The gpu-viv-bin-mx6q package selects BR2_PACKAGE_HAS_OPENGL_EGL and
BR2_PACKAGE_HAS_OPENGL_ES, so when it is enabled, Buildroot believes
that OpenGL and EGL support is available.

However, both libgles.mk and libegl.mk do not add the dependency on
gpu-viv-bin-mx6q, so when pulling the libgles or libegl dependencies,
the build fails due to the absence of an OpenGL implementation. This
commit fixes that.

Fixes the build failure at
http://autobuild.buildroot.org/results/dbd/dbd938914883a9e205f967f7b4b4a8a7dc7be117/build-end.log

.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>