tegra: override compiler flags for low level init code

Override -march setting for tegra to -march=armv4t for files that are
necessary for low level init on tegra.

The recent change to use -march=armv7-a for armv7 caused a regression
on tegra because tegra starts boot on a arm7tdmi processor before
transferring control to the cortex-a9.  While still executing on the
arm7tdmi there are calls to getenv_ulong() and memset() that cause an
illegal instruction exception if compiled for armv7.

Signed-off-by: Allen Martin <amartin@nvidia.com>
Tested-by: Stephen Warren <swarren@wwwdotorg.org>
Signed-off-by: Tom Warren <twarren@nvidia.com>

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

@@ -24,10 +24,13 @@
 # MA 02111-1307 USA
 #
 
-# Tegra has an ARMv4T CPU which runs board_init_f(), so we must build this
-# file with compatible flags
+# Tegra has an ARMv4T CPU which runs board_init_f(), so we must build these
+# files with compatible flags
 ifdef CONFIG_TEGRA2
 CFLAGS_arch/arm/lib/board.o += -march=armv4t
+CFLAGS_arch/arm/lib/memset.o += -march=armv4t
+CFLAGS_lib/string.o += -march=armv4t
+CFLAGS_common/cmd_nvedit.o += -march=armv4t
 endif
 
 USE_PRIVATE_LIBGCC = yes