drm/i915/uc: HuC firmware can't be supported without GuC

There is no point in selecting HuC firmware if GuC is unsupported
or it was already disabled, as we need GuC to authenticate HuC.

While around, make uc_fw_init_early work without direct access
to whole i915, pass only needed platform/rev info.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190807170034.8440-3-michal.wajdeczko@intel.com