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/pinephone_defconfig b/configs/pinephone_defconfig
index 9d39204..ae60943 100644
--- a/configs/pinephone_defconfig
+++ b/configs/pinephone_defconfig
@@ -10,6 +10,7 @@
 CONFIG_MMC_SUNXI_SLOT_EXTRA=2
 CONFIG_PINEPHONE_DT_SELECTION=y
 # CONFIG_SYS_MALLOC_CLEAR_ON_INIT is not set
+CONFIG_SYS_PBSIZE=1024
 CONFIG_OF_LIST="sun50i-a64-pinephone-1.1 sun50i-a64-pinephone-1.2"
 CONFIG_LED_STATUS=y
 CONFIG_LED_STATUS_GPIO=y