drm/i915/acpi: Move the code to populate ACPI device ID into intel_acpi

Move the code that populates the ACPI device ID for devices, into more
appripriate intel_acpi.c. This is done in preparation for more users of
this code.

Signed-off-by: Rajat Jain <rajatja@google.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191220200353.252399-1-rajatja@google.com