rockchip: rk3288: Move rk3288_detect_reset_reason to soc file

The rk3288_detect_reset_reason() is per-SoC operation, move
it to rk3288.c, and extend the rk_board_late_init() with
rk3288_board_late_init() to make all the board works fine
as before.

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>