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/imx8mn_bsh_smm_s2pro_defconfig b/configs/imx8mn_bsh_smm_s2pro_defconfig
index b7470ec..655dfbe 100644
--- a/configs/imx8mn_bsh_smm_s2pro_defconfig
+++ b/configs/imx8mn_bsh_smm_s2pro_defconfig
@@ -36,6 +36,7 @@
 CONFIG_SPL_WATCHDOG=y
 CONFIG_SYS_PROMPT="> "
 CONFIG_SYS_MAXARGS=64
+CONFIG_SYS_CBSIZE=2048
 CONFIG_SYS_PBSIZE=2067
 CONFIG_CMD_FUSE=y
 CONFIG_CMD_MMC=y