backlight: apple_bl: Convert to a platform driver

backlight: apple_bl: Convert to a platform driver

In all cases in which a struct acpi_driver is used for binding a driver
to an ACPI device object, a corresponding platform device is created by
the ACPI core and that device is regarded as a proper representation of
underlying hardware.  Accordingly, a struct platform_driver should be
used by driver code to bind to that device.  There are multiple reasons
why drivers should not bind directly to ACPI device objects [1].

Overall, it is better to bind drivers to platform devices than to their
ACPI companions, so convert the Apple Backlight ACPI driver to a
platform one.

While this is not expected to alter functionality, it changes sysfs
layout and so it will be visible to user space.

Link: https://lore.kernel.org/all/2396510.ElGaqSPkdT@rafael.j.wysocki/
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Daniel Thompson (RISCstar) <danielt@kernel.org>
Link: https://patch.msgid.link/5084777.GXAFRqVoOG@rafael.j.wysocki
Signed-off-by: Lee Jones <lee@kernel.org>