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/ids8313_defconfig b/configs/ids8313_defconfig
index 7415b11..c885de7 100644
--- a/configs/ids8313_defconfig
+++ b/configs/ids8313_defconfig
@@ -140,6 +140,7 @@
 CONFIG_MISC_INIT_R=y
 CONFIG_HUSH_PARSER=y
 # CONFIG_AUTO_COMPLETE is not set
+CONFIG_SYS_CBSIZE=1024
 CONFIG_CMD_IMLS=y
 CONFIG_CMD_ENV_FLAGS=y
 CONFIG_CMD_I2C=y