rockchip: spl: use spl_early_init() instead of spl_init()

Rockchip spl driver needs using spl_early_init().

Fixes: b3d2861e (spl: Remove overwrite of relocated malloc limit)
Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Simon Glass <sjg@chromium.org>