rockchip: evb-rk3288: Drop explicit SPL_TEXT

SPL_TEXT_BASE is 0x0 by default, based on the kconfig
definition move in below commit.

"configs: move CONFIG_SPL_TEXT_BASE to Kconfig"
(sha1: f89d6133)

So, don't define it explicitly.

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