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/Sinovoip_BPI_M3_defconfig b/configs/Sinovoip_BPI_M3_defconfig
index d27f495..23240a1 100644
--- a/configs/Sinovoip_BPI_M3_defconfig
+++ b/configs/Sinovoip_BPI_M3_defconfig
@@ -17,6 +17,7 @@
 CONFIG_SATAPWR="PD25"
 # CONFIG_SYS_MALLOC_CLEAR_ON_INIT is not set
 CONFIG_CONSOLE_MUX=y
+CONFIG_SYS_PBSIZE=1024
 CONFIG_PHY_REALTEK=y
 CONFIG_SUN8I_EMAC=y
 CONFIG_AXP_DCDC5_VOLT=1200