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/mx7ulp_evk_plugin_defconfig b/configs/mx7ulp_evk_plugin_defconfig
index f29ecf6..ea03eb3 100644
--- a/configs/mx7ulp_evk_plugin_defconfig
+++ b/configs/mx7ulp_evk_plugin_defconfig
@@ -17,6 +17,7 @@
 CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_MAXARGS=256
+CONFIG_SYS_CBSIZE=512
 CONFIG_SYS_PBSIZE=532
 CONFIG_CMD_MEMTEST=y
 CONFIG_CMD_FUSE=y