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/mx53loco_defconfig b/configs/mx53loco_defconfig
index 7cf959b..bede23d 100644
--- a/configs/mx53loco_defconfig
+++ b/configs/mx53loco_defconfig
@@ -23,6 +23,7 @@
 CONFIG_SYS_CONSOLE_IS_IN_ENV=y
 CONFIG_SYS_CONSOLE_OVERWRITE_ROUTINE=y
 CONFIG_HUSH_PARSER=y
+CONFIG_SYS_PBSIZE=532
 CONFIG_CMD_BOOTZ=y
 CONFIG_CMD_DM=y
 CONFIG_CMD_MMC=y