video: Let video targets optionally decide their default OpenGL configs.

This is necessary because the Raspberry Pi is a strange beast, that believes
it has OpenGL support (through glX?) but generally has GLES2 support.

So when using the raspberry video target, we need to force this to default
to a GLES2 context, or by default SDL_CreateWindow() will fail, deep down
when it tries to load the proper GL library.

Fixes testsprite2 (and basically everything else that wasn't testgles2) when
run on a Raspberry Pi without a X server.

Please note that other targets might also need this filled in, the Raspberry
Pi is just the most prominent and readily-available System-On-A-Chip style
thing on my desk.  :)

src/video/raspberry/SDL_rpivideo.c

@@ -123,6 +123,7 @@ RPI_Create()
     device->GL_GetSwapInterval = RPI_GLES_GetSwapInterval;
     device->GL_SwapWindow = RPI_GLES_SwapWindow;
     device->GL_DeleteContext = RPI_GLES_DeleteContext;
+    device->GL_DefaultProfileConfig = RPI_GLES_DefaultProfileConfig;
 
     device->PumpEvents = RPI_PumpEvents;