Load eglIntOpenMAXILDoneMarker() explicitely via dlsym()  instead of having a stub in libEGL and libbcm_host

...ng a stub in libEGL and libbcm_host

This fixes linking problems caused by "wrong" linking order and especially
makes this work reliable if libopenmaxil is loaded via dlopen().

https://github.com/raspberrypi/firmware/issues/158