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/Cubieboard4_defconfig b/configs/Cubieboard4_defconfig
index 04ed79a..82b3ac1 100644
--- a/configs/Cubieboard4_defconfig
+++ b/configs/Cubieboard4_defconfig
@@ -12,5 +12,6 @@
 CONFIG_USB1_VBUS_PIN="PH14"
 CONFIG_USB3_VBUS_PIN="PH15"
 CONFIG_AXP_GPIO=y
+CONFIG_SYS_PBSIZE=1024
 CONFIG_SYS_I2C_SUN8I_RSB=y
 CONFIG_AXP809_POWER=y