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/minnowmax_defconfig b/configs/minnowmax_defconfig
index c051e00..87eb82a 100644
--- a/configs/minnowmax_defconfig
+++ b/configs/minnowmax_defconfig
@@ -32,6 +32,7 @@
 CONFIG_LAST_STAGE_INIT=y
 CONFIG_MISC_INIT_R=y
 CONFIG_HUSH_PARSER=y
+CONFIG_SYS_PBSIZE=532
 CONFIG_CMD_CPU=y
 CONFIG_CMD_GPIO=y
 CONFIG_CMD_MMC=y