i2c: cros-ec-tunnel: Make the device acpi compatible

Add ACPI entry and use device_property_read to get fw value
which is common to both dtsi and acpi.

Signed-off-by: Akshu Agrawal <akshu.agrawal@amd.com>
Acked-by: Raul E Rangel <rrangel@chromium.org>
Reviewed-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>