dt-bindings: Drop unnecessary *-supply schemas properties

*-supply properties are always a single phandle, so binding schemas
don't need a type $ref nor 'maxItems'.

A meta-schema check for this is pending once these existing cases are
fixed.

Cc: Jonathan Cameron <jic23@kernel.org>
Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: dri-devel@lists.freedesktop.org
Cc: linux-iio@vger.kernel.org
Cc: linux-input@vger.kernel.org
Cc: linux-media@vger.kernel.org
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Acked-by: Lee Jones <lee.jones@linaro.org>
Acked-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20201221234659.824881-1-robh@kernel.org


Signed-off-by: Rob Herring <robh@kernel.org>