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/ea-lpc3250devkitv2_defconfig b/configs/ea-lpc3250devkitv2_defconfig
index f76ce58..bba3755 100644
--- a/configs/ea-lpc3250devkitv2_defconfig
+++ b/configs/ea-lpc3250devkitv2_defconfig
@@ -18,6 +18,7 @@
 # CONFIG_USE_BOOTCOMMAND is not set
 CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_SYS_PROMPT="EA-LPC3250v2=> "
+CONFIG_SYS_CBSIZE=256
 CONFIG_SYS_PBSIZE=288
 CONFIG_CMD_GPIO=y
 CONFIG_CMD_I2C=y