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/octeon_nic23_defconfig b/configs/octeon_nic23_defconfig
index 4137c61..5330915 100644
--- a/configs/octeon_nic23_defconfig
+++ b/configs/octeon_nic23_defconfig
@@ -25,6 +25,7 @@
 CONFIG_BOARD_LATE_INIT=y
 CONFIG_LAST_STAGE_INIT=y
 CONFIG_HUSH_PARSER=y
+CONFIG_SYS_CBSIZE=256
 CONFIG_SYS_PBSIZE=276
 # CONFIG_CMD_FLASH is not set
 CONFIG_CMD_GPIO=y