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/m53menlo_defconfig b/configs/m53menlo_defconfig
index cfaa0e1..a1a5664 100644
--- a/configs/m53menlo_defconfig
+++ b/configs/m53menlo_defconfig
@@ -35,6 +35,7 @@
 CONFIG_SPL_NAND_SUPPORT=y
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_MAXARGS=32
+CONFIG_SYS_CBSIZE=1024
 CONFIG_CMD_ASKENV=y
 CONFIG_CMD_GREPENV=y
 CONFIG_CMD_DM=y