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/zynq_cse_nand_defconfig b/configs/zynq_cse_nand_defconfig
index a26fe83..d21ca55 100644
--- a/configs/zynq_cse_nand_defconfig
+++ b/configs/zynq_cse_nand_defconfig
@@ -26,6 +26,7 @@
 # CONFIG_AUTO_COMPLETE is not set
 # CONFIG_SYS_LONGHELP is not set
 CONFIG_SYS_MAXARGS=32
+CONFIG_SYS_CBSIZE=1024
 CONFIG_SYS_PBSIZE=1047
 # CONFIG_CMD_BDI is not set
 # CONFIG_CMD_CONSOLE is not set