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/stout_defconfig b/configs/stout_defconfig
index 5338ca9..46b2549 100644
--- a/configs/stout_defconfig
+++ b/configs/stout_defconfig
@@ -36,6 +36,7 @@
 CONFIG_SYS_SPI_U_BOOT_OFFS=0x140000
 CONFIG_SPL_YMODEM_SUPPORT=y
 CONFIG_HUSH_PARSER=y
+CONFIG_SYS_CBSIZE=256
 CONFIG_SYS_PBSIZE=256
 CONFIG_CMD_BOOTZ=y
 # CONFIG_CMD_IMI is not set