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/sama5d2_icp_qspiflash_defconfig b/configs/sama5d2_icp_qspiflash_defconfig
index 8846246..ca5787b 100644
--- a/configs/sama5d2_icp_qspiflash_defconfig
+++ b/configs/sama5d2_icp_qspiflash_defconfig
@@ -27,6 +27,7 @@
 CONFIG_DISPLAY_BOARDINFO_LATE=y
 CONFIG_MISC_INIT_R=y
 CONFIG_HUSH_PARSER=y
+CONFIG_SYS_CBSIZE=256
 CONFIG_SYS_PBSIZE=276
 CONFIG_CMD_CONFIG=y
 CONFIG_CMD_BOOTZ=y