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/p2571_defconfig b/configs/p2571_defconfig
index 2df2979..b4e14ad 100644
--- a/configs/p2571_defconfig
+++ b/configs/p2571_defconfig
@@ -15,6 +15,7 @@
 CONFIG_SYS_STDIO_DEREGISTER=y
 CONFIG_SYS_PROMPT="Tegra210 (P2571) # "
 CONFIG_SYS_MAXARGS=64
+CONFIG_SYS_PBSIZE=2084
 # CONFIG_CMD_IMI is not set
 CONFIG_CMD_DFU=y
 CONFIG_CMD_GPIO=y