Avoid modifying the fb_ops via info->fbops to let us make the pointer
const in the future. Drop the unnecessary EXPORT_SYMBOL() while at it.

Cc: linux-fbdev@vger.kernel.org
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/51f55c02ea4057cc46335ca5c447b92a55383f77.1575390740.git.jani.nikula@intel.com