rockchip: enable SPL_LIBGENERIC for rk3036 based boards

function board_init_f_init_reserve will call memset, which
is implemented in lib, and enabled by CONFIG_SPL_LIBGENERIC_SUPPORT
in spl stage.
To reduce the code size, also enable SPL_TINY_MEMSET.
As rk3036 will return to bootrom immediately after dram
initialization, there is no need to run DM, so disable
SPL_DM_SERIAL.

Signed-off-by: Andy Yan <andy.yan@rock-chips.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Acked-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>