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/smdkc100_defconfig b/configs/smdkc100_defconfig
index e03abd1..d4d45c9 100644
--- a/configs/smdkc100_defconfig
+++ b/configs/smdkc100_defconfig
@@ -20,6 +20,7 @@
 CONFIG_HUSH_PARSER=y
 # CONFIG_AUTO_COMPLETE is not set
 CONFIG_SYS_PROMPT="SMDKC100 # "
+CONFIG_SYS_CBSIZE=256
 CONFIG_SYS_PBSIZE=384
 # CONFIG_CMD_FLASH is not set
 CONFIG_CMD_ONENAND=y