arm: Tegra2: Add basic NVIDIA Tegra2 SoC support

arch/arm/cpu/armv7/tegra2/Makefile

arch/arm/cpu/armv7/tegra2/board.c

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

arch/arm/cpu/armv7/tegra2/lowlevel_init.S

arch/arm/cpu/armv7/tegra2/sys_info.c

arch/arm/cpu/armv7/tegra2/timer.c

arch/arm/include/asm/arch-tegra2/clk_rst.h

arch/arm/include/asm/arch-tegra2/pinmux.h

arch/arm/include/asm/arch-tegra2/pmc.h

arch/arm/include/asm/arch-tegra2/sys_proto.h

arch/arm/include/asm/arch-tegra2/tegra2.h

arch/arm/include/asm/arch-tegra2/uart.h

board/nvidia/common/board.c