drm/i915: Downgrade scare message for unknown HuC firmware

If we haven't shipped and enabled firmware for a particular platform,
there is nothing the user can do about it. Don't scare the user with an
unactionable, unidentifiable warning!

<6> [310.769452] i915 0000:00:02.0: GuC: No firmware known for this platform!
<4> [310.769458] [drm] HuC: No firmware known for this platform!

Unify both GuC/HuC messages to include the device for which we lack the
firmware, and provide the platform name as an aide-memoire.

v2: Move and refine the message to common site of intel_uc_fw_fetch.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Reviewed-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190108150246.1471-1-chris@chris-wilson.co.uk