ARM: dts: am335x-phycore-som: Remove underscore in node names.

Remove underscore in node names following conventions.

Signed-off-by: Steffen Hemer <s.hemer@phytec.de>
Message-Id: <20230214132302.39087-6-s.hemer@phytec.de>
Signed-off-by: Tony Lindgren <tony@atomide.com>