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/imx8mp_dhcom_pdk2_defconfig b/configs/imx8mp_dhcom_pdk2_defconfig
index fd0d19b..3ef5dc0 100644
--- a/configs/imx8mp_dhcom_pdk2_defconfig
+++ b/configs/imx8mp_dhcom_pdk2_defconfig
@@ -55,6 +55,7 @@
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_PROMPT="u-boot=> "
 CONFIG_SYS_MAXARGS=64
+CONFIG_SYS_CBSIZE=2048
 CONFIG_SYS_PBSIZE=2081
 # CONFIG_BOOTM_NETBSD is not set
 # CONFIG_BOOTM_PLAN9 is not set