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/x530_defconfig b/configs/x530_defconfig
index 860cb22..0c2168b 100644
--- a/configs/x530_defconfig
+++ b/configs/x530_defconfig
@@ -28,6 +28,7 @@
 CONFIG_MISC_INIT_R=y
 CONFIG_SPL_BOARD_INIT=y
 CONFIG_SPL_WATCHDOG=y
+CONFIG_SYS_PBSIZE=276
 CONFIG_CMD_MEMINFO=y
 # CONFIG_CMD_FLASH is not set
 CONFIG_CMD_GPIO=y