odroid-libgl: Move files to /opt with ld.conf.so.d entry, and do not conflict with mesa-libgl

Moving installation of odroid-libgl libraries to /opt with a proper ld.conf.so.d entry shadows mesa's libegl and libgles, and allows mesa-libgl to still provide a software fallback for libGL (which some packages cannot replace with libGLES/libEGL).

Tested with es2_info/es2gears_x11, and verified with 'ldd' to properly link and use odroid-libgl's libraries over mesa-libgl's.