arm64: dts: imx8mp-beacon-kit: Fix errors found from CHECK_DTBS

arm64: dts: imx8mp-beacon-kit: Fix errors found from CHECK_DTBS

The adv7535 has some unnecessary entries which can be removed since
they were not setup properly anyway and the defaults work just fine.
Removing them and adding some required regulators make the errors
detected from CHECK_DTBS go away:

 reg-names:1: 'edid' was expected
 reg-names:2: 'cec' was expected
 'avdd-supply' is a required property
 'dvdd-supply' is a required property
 'pvdd-supply' is a required property
 'a2vdd-supply' is a required property
 'v3p3-supply' is a required property

Signed-off-by: Adam Ford <aford173@gmail.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>