Let's drop the last two remaining omap3 legacy boot board files.
Let's only use the device tree based booting known to work for
these two boards.

We still have two omap3 boards booting in legacy mode in addition
to device tree based booting. All the other ten or so omap2+ SoCs
have been booting using device tree mode only for years now. This
has allowed us to get rid of quite a bit of arch/arm/mach-omap2
related platform init code in favor of dts and driver changes.

Pretty much the only remaining known users for omap3 legacy boot
board files are Kevin's and Russell's boot test systems, and N900
kernel tree maintained by Pali and Ivaylo. And all of them are
also supporting the device tree based booting. The legacy booting
mode has been kept around mostly to verify against regressions.

As there is still a slim chance of possible other uses of the
mainline kernel for these boards, let's just drop the board
files for v4.8, and let's not touch the related platform init
code until around v4.9 time if no issues are found. This makes
it trivial for us to add back the board files with a simple revert.
Signed-off-by: Tony Lindgren <tony@atomide.com>