ARM: uniphier: merge board init functions into board_init()

Currently, the UniPhier platform calls several init functions in the
following order:

  [1] spl_board_init()
  [2] board_early_init_f()
  [3] board_init()
  [4] board_early_init_r()
  [5] board_late_init()

The serial console is not ready at the point of [2], so we want to
avoid using [2] from the view point of debuggability.  Fortunately,
all of the initialization in [2] can be delayed until [3].  I see no
good reason to split into [3] and [4].  So, merge [2] through [4].

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