MFC r310593,r310599:

r310593:
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.
r310599:
Import drm_patform.c, an implementation of non-PCI based attachment for
graphics drivers. It will be used in upcoming driver for Nvidia Tegra
boards.