odroid-mali: fix broken headers

Upstream has updated the OpenGL
headers (https://github.com/mdrjr/c2_mali/issues/1) it should fix
failures such as:

  http://autobuild.buildroot.net/results/ed8d562ae5fdb472a83f9a07b2f755c80c972c34/



in addition, when the framebuffer variant (i.e not X11) is used, we
update the cflags in egl.pc to pass -DMESA_EGL_NO_X11_HEADERS so that
X11 headers are not included.

Reported-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Dagg Stompler <daggs@gmx.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>