egl: reset blob cache set/get functions on terminate

Fixes errors seen with eglSetBlobCacheFuncsANDROID on Android when running dEQP that terminates and reinitializes a display.

Fixes: 6f5b5709 "egl: add support for EGL_ANDROID_blob_cache" Signed-off-by: Tapani Pälli tapani.palli@intel.com