ACPI: scan: Eliminate __acpi_device_add()

Instead of having acpi_device_add() defined as a wrapper around
__acpi_device_add(), export acpi_tie_acpi_dev() so it can be called
directly by acpi_add_power_resource(), fold acpi_device_add() into the
latter and rename __acpi_device_add() to acpi_device_add().

No intentional functional impact.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Punit Agrawal <punit.agrawal@bytedance.com>