Documentation: remove :numbered: from lower level toctrees ...

Only the highest level toctree may have :numbered:, otherwise
sphinxs complains loudly that the subtree is already numbered.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Documentation: fix am335x title ...

Fixes:
Documentation/boards/am335x.rst:51: WARNING: Title underline too short.

Signed-off-by: Robert Schwebel <r.schwebel@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Docs: Add phytec-som-am335x documentation ...

Signed-off-by: Wadim Egorov <w.egorov@phytec.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Documentation: Add some TI AM335x specific documentation ...

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>