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/total_compute_defconfig b/configs/total_compute_defconfig
index 64a637e..1a674de 100644
--- a/configs/total_compute_defconfig
+++ b/configs/total_compute_defconfig
@@ -23,6 +23,7 @@
 CONFIG_AVB_BUF_SIZE=0x10000000
 CONFIG_SYS_PROMPT="TOTAL_COMPUTE# "
 CONFIG_SYS_MAXARGS=64
+CONFIG_SYS_CBSIZE=512
 CONFIG_SYS_PBSIZE=544
 # CONFIG_CMD_CONSOLE is not set
 # CONFIG_CMD_XIMG is not set