soc/intel/skylake: Get rid of device_t

Use of device_t has been abandoned in ramstage.

Change-Id: Idf00c029331aba30c8bfca71546cad62ff6bb0a7
Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/26541
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
8 files changed