drm/i915/guc: Combine enable_guc_loading|submission modparams

We currently have two module parameters that control GuC:
"enable_guc_loading" and "enable_guc_submission". Whenever
we need submission=1, we also need loading=1. We also need
loading=1 when we want to want to load and verify the HuC.

Lets combine above module parameters into one "enable_guc"
modparam. New supported bit values are:

 0=disable GuC (no GuC submission, no HuC)
 1=enable GuC submission
 2=enable HuC load

Special value "-1" can be used to let driver decide what
option should be enabled for given platform based on
hardware/firmware availability or preference.

Explicit enabling any of the GuC features makes GuC load
a required step, fallback to non-GuC mode will not be
supported.

v2: Don't use -EIO
v3: define modparam bits (Chris)
v4: rely on implicit cast (Chris)

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Sagar Arun Kamble <sagar.a.kamble@intel.com>
Cc: Sujaritha Sundaresan <sujaritha.sundaresan@intel.com>
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/20171206135316.32556-6-michal.wajdeczko@intel.com