rockchip: configs: mk808: change CONFIG_TPL_TEXT_BASE

Currently the Rockchip rk3066a u-boot-tpl.bin file needs
to add the characters "RK30", while the other SoCs replace
the first 4 bytes. Bring this in line with the rest by
lowering CONFIG_TPL_TEXT_BASE and update rockchip.rst
instructions.

Signed-off-by: Johan Jonker <jbx6244@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
diff --git a/configs/mk808_defconfig b/configs/mk808_defconfig
index c080706..5a264eb 100644
--- a/configs/mk808_defconfig
+++ b/configs/mk808_defconfig
@@ -18,7 +18,7 @@
 CONFIG_DM_RESET=y
 CONFIG_ROCKCHIP_RK3066=y
 # CONFIG_ROCKCHIP_STIMER is not set
-CONFIG_TPL_TEXT_BASE=0x10080C04
+CONFIG_TPL_TEXT_BASE=0x10080c00
 CONFIG_TPL_STACK=0x1008FFFF
 CONFIG_TARGET_MK808=y
 CONFIG_SPL_STACK_R_ADDR=0x70000000