arm: mvebu: Do not call board_init_r() from board_init_f()

arm: mvebu: Do not call board_init_r() from board_init_f()

Instead of calling board_init_r() directly from board_init_f(), just
return from board_init_f(). This will make the code continue executing
in crt0.S _main(), from which the board_init_r() is called. This patch
aligns the MVEBU SPL with the correct SPL design as well as reduces
the stack utilisation slightly.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Marek Vasut <marex@denx.de>
Cc: Simon Glass <sjg@chromium.org>
Cc: Luka Perkov <luka.perkov@sartura.hr>