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/o4-imx6ull-nano_defconfig b/configs/o4-imx6ull-nano_defconfig
index 158caf1..b634a82 100644
--- a/configs/o4-imx6ull-nano_defconfig
+++ b/configs/o4-imx6ull-nano_defconfig
@@ -9,6 +9,7 @@
 CONFIG_IMX_MODULE_FUSE=y
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_MAXARGS=32
+CONFIG_SYS_PBSIZE=532
 CONFIG_CMD_BOOTZ=y
 CONFIG_CMD_MEMINFO=y
 CONFIG_CMD_MEMTEST=y