moveconfig: prepare moving CONFIG_SYS_SPI_U_BOOT_OFFS to Kconfig step 1

Some boards have coded this offset with formula or bitshifts in their
board-config. Manually convert these things into hex-values to be able
using moveconfig.py afterwards.

Signed-off-by: Hannes Schmelzer <hannes.schmelzer@br-automation.com>
diff --git a/doc/README.rockchip b/doc/README.rockchip
index ab3361a..531a062 100644
--- a/doc/README.rockchip
+++ b/doc/README.rockchip
@@ -559,7 +559,7 @@
 offset 128KB and the whole image is padded to 4MB which is the SPI flash size.
 The position of U-Boot is controlled with this setting in U-Boot:
 
-   #define CONFIG_SYS_SPI_U_BOOT_OFFS	(128 << 10)
+   #define CONFIG_SYS_SPI_U_BOOT_OFFS	0x20000
 
 If you have a Dediprog em100pro connected then you can write the image with: