tegra2: Always build with USE_PRIVATE_LIBGCC=yes.

The AVP on Tegra2 doesn't boot properly when U-Boot is linked against
the GCC provided libgcc. To work around this, always build and link
against a private libgcc for Tegra2-based boards.
Signed-off-by: NThierry Reding <thierry.reding@avionic-design.de>
Tested-by: NSimon Glass <sjg@chromium.org>
Signed-off-by: NTom Warren <twarren@nvidia.com>

arch/arm/cpu/armv7/tegra2/config.mk

@@ -29,3 +29,5 @@
 ifdef CONFIG_TEGRA2
 CFLAGS_arch/arm/lib/board.o += -march=armv4t
 endif
+
+USE_PRIVATE_LIBGCC = yes