ARM: uniphier: update DRAM init code for LD20 SoC (2nd)

- Do not reference CONFIG_DDR_FREQ; now the DDR frequency
    is passed from the uniphier_board_data structure
  - Constify parameter arrays
  - Tidy up cluttered macros
  - Lots of code cleanups
  - Lots of coding style fixes

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