Bug#803159: linux: Enable DT support for armel/orion5x arch

[Roger Shimizu <rogershimizu@gmail.com>]

I have good news.

> If you can figure out why the LS-WTGL doesn't work and that can be
> fixed (i.e. it turns out to be something other than the size) then I
> see no problem with adding support for the LS-WTGL platform.

I finished "git bisect" and good commit is 1553282b11e and bad one is
c544d987d9572 (in debian kernel repo).
So 3.19.3-1~exp2 is bootable, but 4.0-1~exp1 is non-bootable.
I compared the configs, and find former has DEBUG_ICEDCC and latter
has DEBUG_LL_UART_NONE.
I also find it's not possible to set DEBUG_LL_UART_NONE for 4.0 kernel.
After some searches, I tried to set DEBUG_LL_UART_8250 for 4.0 kernel,
then the kernel became bootable on my orion5x device!

I also find evidences this change is necessary starting for new 4.x kernel:
1. kirkwood changed from 3.16's DEBUG_LL_UART_NONE to 4.x's
DEBUG_MVEBU_UART0_ALTERNATE: commit bf56620e4 and 58669ce1 (in debian
kernel repo)
2. mainline kernel changed to DEBUG_LL_UART_8250 for orion5x arch:
commit 34c64a5d8 (in upstream repo)

So I think it's now safe to turn on DEBUG_LL_UART_8250 and merge my patch.
Thank you!

Cheers,
Roger