[U-Boot] Unifying device tree filenames, and U-Boot SoC name

[Stephen Warren]

I just posted a patch which causes U-Boot to define some variables
describing which board you're running on:

http://lists.denx.de/pipermail/u-boot/2012-May/124556.html

In particular, see the description of that first patch for motivation
re: U-Boot scripts.

The one issue here is that the U-Boot SoC name for Tegra20 is tegra2
(hence it will define board_soc=tegra2), whereas the kernel's device
tree files are all tegra-*.dts not tegra2-*.dts.

I propose we fix this by:

a) In the kernel, renaming tegra*-${board}.dts to tegra20-${board}.dts
(or tegra30-${board}.dts). This appears to better match what most other
ARM sub-arches are doing anyway.

b) In U-Boot, rename the tegra2 support to tegra20 so that U-Boot ends
up setting board_soc=tegra20, so this matches the .dts/.dtb filenames.
This would involve renaming arch/arm/cpu/armv7/tegra2/ to
./arch/arm/cpu/armv7/tegra20/ and editing boards.cfg to match, and
possibly other related changes.

This sounds like churn, but I think we could easily fold this into
Allen's series that moves the tegra2 directory in order to put it in a
common place for separate SPL/non-SPL builds to avoid doing this kind of
thing multiple times.

Does anyone think this is a good/bad/... idea? Thanks.