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/ge_bx50v3_defconfig b/configs/ge_bx50v3_defconfig
index 6d5496c..c9e4ee8 100644
--- a/configs/ge_bx50v3_defconfig
+++ b/configs/ge_bx50v3_defconfig
@@ -24,6 +24,7 @@
 CONFIG_LAST_STAGE_INIT=y
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_MAXARGS=32
+CONFIG_SYS_PBSIZE=532
 CONFIG_CMD_BOOTZ=y
 CONFIG_CMD_DM=y
 # CONFIG_CMD_FLASH is not set