egl/drm: expose KHR_image_pixmap extension

This changes enables EGL_KHR_image_pixmap in the egl drm platform, which is implemented
there but has not been advertised yet.

Cc: 10.2 10.3 <mesa-stable@lists.freedesktop.org>
Signed-off-by: Andreas Pokorny <andreas.pokorny@canonical.com>
Reviewed-by: Daniel Stone <daniels@collabora.com>

src/egl/drivers/dri2/platform_drm.c

@@ -681,6 +681,7 @@ dri2_initialize_drm(_EGLDriver *drv, _EGLDisplay *disp)
                       i + 1, EGL_WINDOW_BIT, attr_list, NULL);
    }
 
+   disp->Extensions.KHR_image_pixmap = EGL_TRUE;
    if (dri2_dpy->dri2)
       disp->Extensions.EXT_buffer_age = EGL_TRUE;