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/colibri_t30_defconfig b/configs/colibri_t30_defconfig
index 1e1a435..5419183 100644
--- a/configs/colibri_t30_defconfig
+++ b/configs/colibri_t30_defconfig
@@ -19,6 +19,7 @@
 CONFIG_ARCH_MISC_INIT=y
 CONFIG_SYS_PROMPT="Colibri T30 # "
 CONFIG_SYS_MAXARGS=32
+CONFIG_SYS_CBSIZE=1024
 CONFIG_SYS_PBSIZE=1055
 # CONFIG_CMD_IMI is not set
 CONFIG_CMD_GPIO=y