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/gazerbeam_defconfig b/configs/gazerbeam_defconfig
index f2f0257..2f3b29e 100644
--- a/configs/gazerbeam_defconfig
+++ b/configs/gazerbeam_defconfig
@@ -130,6 +130,7 @@
 CONFIG_BOARD_EARLY_INIT_R=y
 CONFIG_LAST_STAGE_INIT=y
 CONFIG_HUSH_PARSER=y
+CONFIG_SYS_CBSIZE=1024
 CONFIG_CMD_CPU=y
 CONFIG_CMD_BINOP=y
 CONFIG_CMD_MEMTEST=y