AMD Union Station: Use SPD read code from F14 wrapper

Changes:
 - Get rid of the union_station mainboard specific code and
   use the platform generic function wrapper that was added
   in change http://review.coreboot.org/#/c/2497/
   AMD f14: Add SPD read functions to wrapper code

 - Move DIMM addresses into devicetree.cb

 - Add the ASF init that used to be in the SPD read code into
   mainboard_enable()

Notes:
 - The DIMM reads only happen in romstage, so the function is not
   available in ramstage.  Point the read-SPD callback to a generic
   function in ramstage.

Change-Id: I19d6b0d674b67294519383f80928471b37da1e14
Signed-off-by: Kimarie Hoot <kimarie.hoot@se-eng.com>
Reviewed-on: http://review.coreboot.org/2609
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martin.roth@se-eng.com>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
6 files changed