linux-firmware: Add i915 GuC firmware

linux-firmware: Add i915 GuC firmware

GuC is designed to perform graphics workload scheduling on the various
graphics parallel engines. In this scheduling model, host software
submits work through one of the 256 graphics doorbells and this invokes
the scheduling operation on the appropriate graphics engine. Scheduling
operations include determining which workload to run next, submitting a
workload to a command streamer, pre-empting existing workloads running
on an engine, monitoring progress and notifying host SW when work is
done.

This is the first release of GuC firmware for Skylake platforms.

skl_guc_ver1.bin is a symbolik link to latest recommended minor release.
This major version will be just upgraded on code when it is required
software changes for API/ABI compatibility.

Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>