rockchip: rv1108: use correct API for board callback

Use board_early_init_f() instead of mach_cpu_init() for board, the
board_early_init_f() is used for board init and after dm_initf, while
the mach_cpu_init() is used for CPU/SOC and before dm_initf()(not able
to use syscon API).

Fixes: 9cec3367 ("rockchip: evb-rv1108: Use syscon API to get grf base")
Fixes: 4aa33690 {"rockchip: elgin-rv1108: Use syscon API to get grf base")

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