ARM: tegra: remove CONFIG_MACH_TEGRA_DT

* Make ARCH_TEGRA select USE_OF; DT is the way forward.
* Build board-dt-tegra*.c when the relevant Tegra SoC support is enabled,
  rather than requiring a specific config option for this.
* The board-specific config options already build board-*-pinmux.o, and
  when booting from device tree these files are no longer needed, so we
  can remove some Makefile commands related to those files.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 84449dd..3b24b41 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -645,6 +645,7 @@
 	select MIGHT_HAVE_CACHE_L2X0
 	select NEED_MACH_IO_H if PCI
 	select ARCH_HAS_CPUFREQ
+	select USE_OF
 	help
 	  This enables support for NVIDIA Tegra based systems (Tegra APX,
 	  Tegra 6xx and Tegra 2 series).