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/iNet_D978_rev2_defconfig b/configs/iNet_D978_rev2_defconfig
index 9a90252..339e9f6 100644
--- a/configs/iNet_D978_rev2_defconfig
+++ b/configs/iNet_D978_rev2_defconfig
@@ -17,6 +17,7 @@
 CONFIG_VIDEO_LCD_BL_PWM="PH0"
 CONFIG_VIDEO_LCD_PANEL_LVDS=y
 # CONFIG_SYS_MALLOC_CLEAR_ON_INIT is not set
+CONFIG_SYS_PBSIZE=1024
 CONFIG_AXP_DLDO1_VOLT=3300
 # CONFIG_REQUIRE_SERIAL_CONSOLE is not set
 CONFIG_CONS_INDEX=5