rockchip: Add support for chromebook_bob

Bob is a 10-inch chromebook produced by Asus. It has two USB 3.0 type-C
ports, 4GB of SDRAM, WiFi and a 1280x800 display. It uses its USB ports
for both power and external display. It includes a Chrome OS EC
(Cortex-M3) to provide access to the keyboard and battery functions.

Support so far includes only:
- UART
- SDRAM
- MMC, SD card
- Cros EC (but not keyboard)

Not included:
- Keyboard
- Display
- Sound
- USB
- TPM

Bob is quite similar to Kevin, the Samsung Chromebook Plus, but support
for this is not provided in this series.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>

doc/README.rockchip

@@ -52,13 +52,14 @@ One RK3328 board is supported:
 
    - EVB RK3328
 
-Five RK3399 boards are supported (aarch64):
+Size RK3399 boards are supported (aarch64):
 
    - EBV RK3399 - use evb_rk3399 configuration
    - Firefly RK3399 - use the firefly_rk3399 configuration
    - Puma - use puma_rk3399 configuration
    - Ficus - use ficus-rk3399 configuration
    - Rock960 (Vamrs) - use rock960-rk3399 configuration
+   - Bob - use chromebook_bob configuration
 
 Four RK3368 boards are supported:
 
@@ -253,7 +254,8 @@ You should see something like:
 Booting from SPI
 ================
 
-To write an image that boots from SPI flash (e.g. for the Haier Chromebook):
+To write an image that boots from SPI flash (e.g. for the Haier Chromebook or
+Bob):
 
    ./chromebook_jerry/tools/mkimage -n rk3288 -T rkspi \
 	-d chromebook_jerry/spl/u-boot-spl-dtb.bin spl.bin && \