drm/i915/guc: Sanitize GuC client initialization

drm/i915/guc: Sanitize GuC client initialization

Started adding proper teardown to guc_client_alloc, ended up removing
quite a few dead ends where errors communicating with the GuC were
silently ignored. There also seemed to be quite a few erronous
teardown actions performed in case of an error (ordering wrong).

v2:
  - Increase function symmetry/proximity (Michal/Daniele)
  - Fix __reserve_doorbell accounting for high priority (Daniele)
  - Call __update_doorbell_desc! (Daniele)
  - Isolate __guc_{,de}allocate_doorbell (Michal/Daniele)

v3:
  - "Select" a cacheline is a more accurate verb than "reserve" (Daniele).
  - We cannot update & create the doorbell without reserving it first, so
    move the whole doorbell creation for execbuf_client to the submission
    enable (Oscar).i
  - Add a fixme for ignoring possible doorbell destroy errors.

v4:
  - Remove comment about is_high_priority (Daniele)
  - Debug message typo (Daniele)
  - Reuse __get_doorbell in more places (Daniele)
  - Do not do arithmetic on void pointers (Daniele)
  - Add comment to __reset_doorbell (Daniele)

v5:
  - gccisms like arithmetic on void pointers are not frowned upon (Oscar)

Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Arkadiusz Hiler <arkadiusz.hiler@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Oscar Mateo <oscar.mateo@intel.com>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>