arm: Tegra2: add support for A9 CPU init

arch/arm/cpu/armv7/start.S

arch/arm/cpu/armv7/tegra2/Makefile

arch/arm/cpu/armv7/tegra2/ap20.c

arch/arm/cpu/armv7/tegra2/ap20.h

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

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

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

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

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

board/nvidia/common/board.c

board/nvidia/common/board.h

include/configs/harmony.h

include/configs/seaboard.h

include/configs/tegra2-common.h