arm: mvebu: a38x: Add optional support for using old DDR3 training code

arm: mvebu: a38x: Add optional support for using old DDR3 training code

Add optional support for using old DDR3 training code from 2017.

The code lives in drivers/ddr/marvell/a38x/old/. To prevent symbol
clashing with new DDR3 training code, a special header which renames all
clashing symbols via macros is included and the symbols are prefixed
with 'old_'.

If old DDR3 training support is selected for a board, then the SPL
initialization code calls a new function
  board_use_old_ddr3_training()
to check whether it should use old DDR3 training code. The default
weak implementation returns false, defaulting to new DDR3 training code.

Boards that wish to support this need to select the
  ARMADA_38X_SUPPORT_OLD_DDR3_TRAINING
config option and implement the old version of DDR topology provider,
ddr3_get_topology_map().

Signed-off-by: Marek Behún <kabel@kernel.org>