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/armadillo-800eva_defconfig b/configs/armadillo-800eva_defconfig
index d4490ea..784064a 100644
--- a/configs/armadillo-800eva_defconfig
+++ b/configs/armadillo-800eva_defconfig
@@ -19,6 +19,7 @@
 CONFIG_BOOTDELAY=3
 # CONFIG_CMDLINE_EDITING is not set
 # CONFIG_AUTO_COMPLETE is not set
+CONFIG_SYS_CBSIZE=256
 CONFIG_SYS_PBSIZE=256
 # CONFIG_CMD_BDI is not set
 # CONFIG_CMD_CONSOLE is not set