opengl: Ensure we only load the GLES emulation library when the emulator supports it.

This patch modifies the libEGL.so loader to only load the emulator-specific
EGL/GLES libraries if it detects at runtime that the emulator supports it.

This prevents the system crashing when booting the platform image under an old
emulator version, or one without GPU emulation enabled.

Change-Id: I711b3f0a4ee1f3b080263780726ce7ec28ff11d6