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/bananapi_m1_plus_defconfig b/configs/bananapi_m1_plus_defconfig
index 2f0c22f..1b5f6ba 100644
--- a/configs/bananapi_m1_plus_defconfig
+++ b/configs/bananapi_m1_plus_defconfig
@@ -10,6 +10,7 @@
 CONFIG_AHCI=y
 # CONFIG_SYS_MALLOC_CLEAR_ON_INIT is not set
 CONFIG_SPL_I2C=y
+CONFIG_SYS_PBSIZE=1024
 CONFIG_NETCONSOLE=y
 CONFIG_SCSI_AHCI=y
 CONFIG_SYS_I2C_MVTWSI=y