package/mesa3d: fix EGL/GLES provider

mesa3d being selected is not enough for it to be an EGL provider.

The corresponding options BR2_PACKAGE_MESA3D_OPENGL_EGL should be
enabled. This option already correctlt selects BR2_PACKAGE_HAS_OPENGL_EGL.

So, only declare mesa3d as an EGL provider if the option is set.

Ditto for GLES.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Bernd Kuhls <berndkuhls@hotmail.com>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>