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/warp7_defconfig b/configs/warp7_defconfig
index 50c4ba0..40f9e50 100644
--- a/configs/warp7_defconfig
+++ b/configs/warp7_defconfig
@@ -24,6 +24,7 @@
 # CONFIG_BOARD_EARLY_INIT_F is not set
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_MAXARGS=32
+CONFIG_SYS_PBSIZE=532
 # CONFIG_CMD_BOOTD is not set
 CONFIG_CMD_BOOTZ=y
 # CONFIG_CMD_IMI is not set