board_f: Introduce arch_setup_bdinfo initcall

Certain architectures (ppc, mips, sh, m68k) use setup board_part1 and
setup_board_part2 calls during pre-relocation init to populate gd->bd
boardinfo fields. This makes the generic init sequence cluttered with
arch-specific ifdefs.

In order to clean these arch-specific sequences from generic init,
introduce arch_setup_bdinfo weak initcall so that everyone can define their
own bdinfo setup routines.

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Ovidiu Panait <ovidiu.panait@windriver.com>