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/pine64-lts_defconfig b/configs/pine64-lts_defconfig
index 7e7c2d7..94c03f1 100644
--- a/configs/pine64-lts_defconfig
+++ b/configs/pine64-lts_defconfig
@@ -10,6 +10,7 @@
 CONFIG_MMC_SUNXI_SLOT_EXTRA=2
 CONFIG_SPL_SPI_SUNXI=y
 # CONFIG_SYS_MALLOC_CLEAR_ON_INIT is not set
+CONFIG_SYS_PBSIZE=1024
 CONFIG_SUPPORT_EMMC_BOOT=y
 CONFIG_SPI_FLASH_WINBOND=y
 CONFIG_SUN8I_EMAC=y