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/beelink_x2_defconfig b/configs/beelink_x2_defconfig
index 6206d90..432079a 100644
--- a/configs/beelink_x2_defconfig
+++ b/configs/beelink_x2_defconfig
@@ -6,5 +6,6 @@
 CONFIG_DRAM_CLK=567
 CONFIG_MMC_SUNXI_SLOT_EXTRA=2
 # CONFIG_SYS_MALLOC_CLEAR_ON_INIT is not set
+CONFIG_SYS_PBSIZE=1024
 CONFIG_SUN8I_EMAC=y
 CONFIG_USB_EHCI_HCD=y