rockchip: rk3368: move STACK_R_ADDR address and into Kconfig

With the STACK_R_ADDR at 0x600000 (6MB) we're competing with
with the loading address of either u-boot or atf parts, so move
that away to 0x4000000 (64MB) similar to rk3399.

Only lion currently sets that at all but not sheep the second
rk3368 board, so just move that to the Kconfig for rk3368 similar
to rk3399 as well.

Signed-off-by: Heiko Stuebner <heiko.stuebner@theobroma-systems.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>