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/xilinx_zynqmp_mini_nand_defconfig b/configs/xilinx_zynqmp_mini_nand_defconfig
index 48a2ff2..dd5a36c 100644
--- a/configs/xilinx_zynqmp_mini_nand_defconfig
+++ b/configs/xilinx_zynqmp_mini_nand_defconfig
@@ -23,6 +23,7 @@
 # CONFIG_AUTO_COMPLETE is not set
 # CONFIG_SYS_LONGHELP is not set
 CONFIG_SYS_MAXARGS=64
+CONFIG_SYS_CBSIZE=1024
 CONFIG_SYS_PBSIZE=1049
 # CONFIG_CMD_BDI is not set
 # CONFIG_CMD_CONSOLE is not set