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/taurus_defconfig b/configs/taurus_defconfig
index 902bfb5..90f9133 100644
--- a/configs/taurus_defconfig
+++ b/configs/taurus_defconfig
@@ -49,6 +49,7 @@
 CONFIG_SPL_DM_SPI_FLASH=y
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_PROMPT="U-Boot> "
+CONFIG_SYS_CBSIZE=256
 CONFIG_SYS_PBSIZE=281
 # CONFIG_SYS_XTRACE is not set
 # CONFIG_CMD_BDI is not set