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/starqltechn_defconfig b/configs/starqltechn_defconfig
index 4d555ce..2d07767 100644
--- a/configs/starqltechn_defconfig
+++ b/configs/starqltechn_defconfig
@@ -15,6 +15,7 @@
 # CONFIG_DISPLAY_CPUINFO is not set
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_MAXARGS=64
+CONFIG_SYS_CBSIZE=512
 CONFIG_SYS_PBSIZE=532
 CONFIG_CMD_GPIO=y
 CONFIG_CMD_BMP=y