dt: dbx5x0: remove mentor,musb binding

dt: dbx5x0: remove mentor,musb binding

The "mentor,musb" binding isn't documented so I was about
to document it.

The node is missing a few properties for configuration like
"multipoint", "dyn_fifo", "num_eps" or "ram_bits". However
I am not sure "missing" is the right word here because some
of those informations might be obtained from the chip itself
but it is not done (yet).

Further the ePARP 2.3.1 says the matching goes from left to
right taking the fist match. Right now there is jus a driver
for "stericsson,db8500-musb" and none for "mentor,musb".
I'm not 100% that it is simply possible to have a generic
since even for DMA we have ifdefs in the driver between
"generic mentor dma" and "ux500 dma" and I mean within musb
and not the dma code.

For that reason (that I am not sure a generic musb binding
is possible and how its binding / required properties will
look like) and the reason that we have here a minor binding
without a driver to look at I suggest to remove that binding.

If the majority of people prefer to keep this binding I'm
curious how the documentation of the binding should look like.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>