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/emsdp_defconfig b/configs/emsdp_defconfig
index 2491183..02dbcb1 100644
--- a/configs/emsdp_defconfig
+++ b/configs/emsdp_defconfig
@@ -13,6 +13,7 @@
 CONFIG_BOARD_EARLY_INIT_R=y
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_PROMPT="emsdp# "
+CONFIG_SYS_CBSIZE=256
 CONFIG_SYS_PBSIZE=280
 # CONFIG_CMD_BOOTD is not set
 # CONFIG_CMD_XIMG is not set