ARM: tegra: Rename board-dt-tegra20.c to tegra.c

This is the preparation to unify "board-dt-tegra{20,30,114}.c" to a
single file "tegra.c".
Signed-off-by: Hiroshi Doyu <hdoyu@nvidia.com>
Signed-off-by: Stephen Warren <swarren@nvidia.com>

arch/arm/mach-tegra/Makefile

@@ -27,7 +27,7 @@ obj-$(CONFIG_HOTPLUG_CPU)               += hotplug.o
 obj-$(CONFIG_CPU_FREQ)                  += cpu-tegra.o
 obj-$(CONFIG_TEGRA_PCI)			+= pcie.o
 
-obj-$(CONFIG_ARCH_TEGRA_2x_SOC)		+= board-dt-tegra20.o
+obj-$(CONFIG_ARCH_TEGRA_2x_SOC)		+= tegra.o
 obj-$(CONFIG_ARCH_TEGRA_3x_SOC)		+= board-dt-tegra30.o
 obj-$(CONFIG_ARCH_TEGRA_114_SOC)	+= board-dt-tegra114.o
 ifeq ($(CONFIG_CPU_IDLE),y)