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/ventana_defconfig b/configs/ventana_defconfig
index 4d9fe46..46d2a55 100644
--- a/configs/ventana_defconfig
+++ b/configs/ventana_defconfig
@@ -14,6 +14,7 @@
 CONFIG_USE_PREBOOT=y
 CONFIG_SYS_PROMPT="Tegra20 (Ventana) # "
 CONFIG_SYS_MAXARGS=64
+CONFIG_SYS_PBSIZE=2085
 # CONFIG_CMD_IMI is not set
 CONFIG_CMD_GPIO=y
 CONFIG_CMD_MMC=y