doc: rockchip: Adapt Pine64 Rock64 board instructions

Now we have our own TPL implementation. Remove obsolete notes.

Signed-off-by: Matwey V. Kornilov <matwey.kornilov@gmail.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
diff --git a/doc/README.rockchip b/doc/README.rockchip
index 8ccbb87..7d4dc1b 100644
--- a/doc/README.rockchip
+++ b/doc/README.rockchip
@@ -309,17 +309,11 @@
 =================================================
 
 For Rock64 rk3328 board the following three parts are required:
-TPL, SPL, and the u-boot image tree blob. While u-boot-spl.bin and
-u-boot.itb are to be compiled as usual, TPL is currently not
-implemented in u-boot, so you need to pick one from rkbin:
-
-  - Get the rkbin
-
-    => git clone https://github.com/rockchip-linux/rkbin.git
+TPL, SPL, and the u-boot image tree blob.
 
   - Create TPL/SPL image
 
-    => tools/mkimage -n rk3328 -T rksd -d rkbin/bin/rk33/rk3328_ddr_333MHz_v1.16.bin idbloader.img
+    => tools/mkimage -n rk3328 -T rksd -d tpl/u-boot-tpl.bin idbloader.img
     => cat spl/u-boot-spl.bin >> idbloader.img
 
   - Write TPL/SPL image at 64 sector