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/hikey_defconfig b/configs/hikey_defconfig
index a769045..9d597b8 100644
--- a/configs/hikey_defconfig
+++ b/configs/hikey_defconfig
@@ -18,6 +18,7 @@
 CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_MISC_INIT_R=y
 CONFIG_SYS_MAXARGS=64
+CONFIG_SYS_CBSIZE=512
 CONFIG_SYS_PBSIZE=532
 CONFIG_CMD_GPIO=y
 CONFIG_CMD_MMC=y