tegra: add new target

New target introduces initial support for NVIDIA Tegra SoC based devices.
It focuses on Tegra 2 CPUs, for successors supporting NEON instruction
set the target should be split in two subtargets.
This initial commit doesn't create any device image, it's groundwork
for further additions.

Signed-off-by: Tomasz Maciej Nowak <tomek_n@o2.pl>

target/linux/tegra/image/generic-bootscript

@@ -0,0 +1,6 @@
+setenv bootargs "root=PARTUUID=@ROOT@-02 rw rootwait console=ttyS0,115200 console=tty0"
+
+load ${devtype} ${devnum}:${bootpart} ${kernel_addr_r} /@KERNEL@
+load ${devtype} ${devnum}:${bootpart} ${fdt_addr_r} /${soc}-${board}.dtb
+
+bootz ${kernel_addr_r} - ${fdt_addr_r}