ARM: OMAP2+: Remove legacy support for omap3 TouchBook

ARM: OMAP2+: Remove legacy support for omap3 TouchBook

We've been moving all omap2+ based systems to boot in device tree only
mode for a few years now. Only omap3 has legacy booting support
remaining. Most omap3 boards already have related arch/arm/boot/*.dts*
files for booting with device tree.

As it seems this board only has minimal support upstreamed for the
legacy booting and has not seen activity for on the mailing lists
for a few years, let's attempt to remove the related legacy board-*.c
file.

I do not have this board, but it seems getting the same level of
support with device tree based booting is mostly just configuring
the .dts file. And there is no need to upgrade the boot loader as
we can boot with appended DTB too. And most of the omap3 boards
seem to be related to omap3-evm, and omap3beagleboard that are
supported with device tree based booting.

If somebody is using this board actively with the mainline kernel,
please communicate this to the linux-omap mailing list so we can
get the board booting with device tree based support. I can help
some too getting the minimal device tree based booting going if
help is needed.

The reason for attempting to remove this board now is that I'd
rather get the remaining omap3 legacy booting support into a known
state where we at least have a .dts file being written for the
remaining legacy boards. That is because for the next few merge
cycles we can still revert this patch if absolutely necessary,
but I'd rather not get suprised by missing .dts files at the point
where we are ready to drop all remaining omap3 legacy booting
support later on.

Cc: Gregoire Gentil <gregoire@gentil.com>
Cc: Radek Pilar <mrkva@mrkva.eu>
Signed-off-by: Tony Lindgren <tony@atomide.com>