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/libretech_all_h3_it_h5_defconfig b/configs/libretech_all_h3_it_h5_defconfig
index cb7ffb4..5bc923a 100644
--- a/configs/libretech_all_h3_it_h5_defconfig
+++ b/configs/libretech_all_h3_it_h5_defconfig
@@ -7,6 +7,7 @@
 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_SPI_FLASH_XMC=y
 CONFIG_SPI=y
 CONFIG_USB_EHCI_HCD=y