T210: Add support for 64-bit T210-based P2571 board

Based on Venice2, incorporates Stephen Warren's
latest P2571 pinmux table.

With Thierry Reding's 64-bit build fixes, this
will build and and boot in 64-bit on my P2571
(when used with a 32-bit AVP loader).

Signed-off-by: Tom Warren <twarren@nvidia.com>
diff --git a/arch/arm/mach-tegra/tegra210/Kconfig b/arch/arm/mach-tegra/tegra210/Kconfig
index f2a0059..147e6a8 100644
--- a/arch/arm/mach-tegra/tegra210/Kconfig
+++ b/arch/arm/mach-tegra/tegra210/Kconfig
@@ -3,9 +3,16 @@
 choice
 	prompt "Tegra210 board select"
 
+config TARGET_P2571
+	bool "NVIDIA Tegra210 P2571 base board"
+	help
+	  P2571 is a P2530 married to a P1963 I/O board
+
 endchoice
 
 config SYS_SOC
 	default "tegra210"
 
+source "board/nvidia/p2571/Kconfig"
+
 endif