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/CHIP_pro_defconfig b/configs/CHIP_pro_defconfig
index 2917960..16456c1 100644
--- a/configs/CHIP_pro_defconfig
+++ b/configs/CHIP_pro_defconfig
@@ -6,6 +6,7 @@
 CONFIG_DRAM_TIMINGS_DDR3_800E_1066G_1333J=y
 CONFIG_USB0_VBUS_PIN="PB10"
 CONFIG_SPL_I2C=y
+CONFIG_SYS_PBSIZE=1024
 # CONFIG_CMD_FLASH is not set
 CONFIG_CMD_MTDPARTS=y
 CONFIG_MTDIDS_DEFAULT="nand0=sunxi-nand.0"