Fix late monitor hotplug event.
If system starts without attached monitor, DRM create framebuffer
for VT console. Later, when monitor is attached, the hotplug event must
issue full modeset procedure to setup CRTC.
In original code, this was done in drm_fb_helper_set_par(), but we don't
have this function implemented yet. Use unrolled version of
drm_fb_helper_set_par() to ensure same functionality.

MFC after: 1 month