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/mx53ppd_defconfig b/configs/mx53ppd_defconfig
index 77551cd..c92e89c 100644
--- a/configs/mx53ppd_defconfig
+++ b/configs/mx53ppd_defconfig
@@ -23,6 +23,7 @@
 CONFIG_MISC_INIT_R=y
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_MAXARGS=48
+CONFIG_SYS_CBSIZE=1024
 CONFIG_CMD_BOOTZ=y
 CONFIG_CMD_DM=y
 CONFIG_CMD_FUSE=y