Convert CONFIG_SYS_CBSIZE to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_CBSIZE

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/at91sam9260ek_dataflash_cs1_defconfig b/configs/at91sam9260ek_dataflash_cs1_defconfig
index e1d8e25..0ad24a2 100644
--- a/configs/at91sam9260ek_dataflash_cs1_defconfig
+++ b/configs/at91sam9260ek_dataflash_cs1_defconfig
@@ -25,6 +25,7 @@
 CONFIG_BOOTCOMMAND="sf probe 0:1; sf read 0x22000000 0x84000 0x294000; bootm 0x22000000"
 # CONFIG_DISPLAY_BOARDINFO is not set
 CONFIG_SYS_PROMPT="U-Boot> "
+CONFIG_SYS_CBSIZE=256
 CONFIG_SYS_PBSIZE=281
 # CONFIG_CMD_BDI is not set
 CONFIG_CMD_BOOTZ=y