ARM: uniphier: update DRAM init code for LD20 SoC

Import the latest version from the Diag software.

  - Support LD21 SoC (including DDR chips in the package)
  - Per-board granule adjustment for both reference and TV boards
  - Misc cleanups

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>