Firmware for White Rabbit on AMD ZCU102 ("Light Rabbit")

Hi,

this MR adds a new board, the AMD ZCU102. No further external hardware is needed, the White Rabbit main and helper clock are tuned using the QPLLs of the GTH transceivers (according to XAPP1276 and as presented by us at the 13th White Rabbit Workshop and White Rabbit Collaboration Launch, slides).

This MR mostly introduces new files. We needed to set the MPLL_FREQ_PRELOCK_GAIN_BOOST to 1 for the splll to lock (in spll_main.c). If there is another way to configure this e.g. in the board config, we are very happy to do so without having to touch any existing files. The board.c is designed to be as generic as possible to simplify development on other boards and be able to re-use this firmware with other boards (e.g. the ZC706).

This MR depends on !20 (merged) to address the various eeproms on the board.

You can find the matching gateware here: wr-cores!18