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/vinco_defconfig b/configs/vinco_defconfig
index 2743b06..280a2ba 100644
--- a/configs/vinco_defconfig
+++ b/configs/vinco_defconfig
@@ -22,6 +22,7 @@
 CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_PROMPT="vinco => "
+CONFIG_SYS_CBSIZE=256
 CONFIG_SYS_PBSIZE=282
 CONFIG_CMD_BOOTZ=y
 # CONFIG_CMD_IMI is not set