rockchip: Add max spl size & spl header configs

Our chips may have different max spl size and spl header, so
we need to add configs for that.

Signed-off-by: Jeffy Chen <jeffy.chen@rock-chips.com>
Acked-by: Simon Glass <sjg@chromium.org>
Dropped CONFIG_ROCKCHIP_MAX_SPL_SIZE from rk3288_common.h,
Added $(if...) to tools/Makefile to fix widespread build breakage
Signed-off-by: Simon Glass <sjg@chromium.org>

Series-changes: 8
- Drop CONFIG_ROCKCHIP_MAX_SPL_SIZE from rk3288_common.h,
- Add $(if...) to tools/Makefile to fix widespread build breakage