Convert CONFIG_SYS_PBSIZE to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_PBSIZE

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/octeontx_81xx_defconfig b/configs/octeontx_81xx_defconfig
index 539ebf1..a92cac3 100644
--- a/configs/octeontx_81xx_defconfig
+++ b/configs/octeontx_81xx_defconfig
@@ -34,6 +34,7 @@
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_PROMPT="Marvell> "
 CONFIG_SYS_MAXARGS=64
+CONFIG_SYS_PBSIZE=1050
 # CONFIG_CMD_BOOTEFI_HELLO_COMPILE is not set
 CONFIG_CMD_MD5SUM=y
 CONFIG_MD5SUM_VERIFY=y