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/pm9263_defconfig b/configs/pm9263_defconfig
index fdc89a9..0013210 100644
--- a/configs/pm9263_defconfig
+++ b/configs/pm9263_defconfig
@@ -21,6 +21,7 @@
 CONFIG_BOARD_EARLY_INIT_F=y
 # CONFIG_AUTO_COMPLETE is not set
 CONFIG_SYS_PROMPT="u-boot-pm9263> "
+CONFIG_SYS_CBSIZE=256
 CONFIG_SYS_PBSIZE=288
 # CONFIG_CMD_BDI is not set
 # CONFIG_CMD_IMI is not set