ARM: dts: am335x-pcm-953: Define fixed regulators in root node

Remove the regulators node and define fixed regulators in the root node.
Prevents the sdhci-omap driver from waiting in probe deferral forever
because of the missing vmmc-supply and keeps am335x-pcm-953 consistent with
the other Phytec AM335 boards.

Fixes: bb07a829 ("ARM: dts: Add support for phyCORE-AM335x PCM-953 carrier board")
Signed-off-by: Dominik Haller <d.haller@phytec.de>
Message-Id: <20221011143115.248003-1-d.haller@phytec.de>
Signed-off-by: Tony Lindgren <tony@atomide.com>