mainboard: Add AMD unionstation RDK support

AMD unionstation Reference Design Kit is Designed for hd settop box application.
This platform using family14 APU, SB800 southbridge.
Vgabios is required, can download vgabios from AMD NDA website.
Verified Feature:
 HDMI, LAN, mini-pcie slots, sata, usb, analog audio and
 optical fiber digital audio output.

Change-Id: Ib1d1d8c889d6fb29f4298b57dfe5c5c1cea1431c
Signed-off-by: Kerry She <kerry.she@amd.com>
Signed-off-by: Kerry She <shekairui@gmail.com>
Reviewed-on: http://review.coreboot.org/434
Tested-by: build bot (Jenkins)
Reviewed-by: Marc Jones <marcj303@gmail.com>
31 files changed