drm/i915/guc: Refactor the concept "GuC context descriptor" into "GuC stage descriptor"

A GuC context and a HW context are in no way related, so the name "GuC context descriptor"
is very unfortunate, because a new reader of the code gets overwhelmed very quickly with
a lot of things called "context" that refer to different things. We can improve legibility
a lot by simply renaming a few objects in the GuC code.

v2:
  - Rebased
  - s/ctx_desc_pool/stage_desc_pool
  - Move some explanations to the definition of the guc_stage_desc struct (Chris)

v3:
  - Calculate gemsize with less intermediate steps (Joonas)
  - Use BIT() macro (Joonas)

Signed-off-by: Oscar Mateo <oscar.mateo@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index e2390df..3ebdbc7 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -2471,8 +2471,8 @@ static void i915_guc_client_info(struct seq_file *m,
 	enum intel_engine_id id;
 	uint64_t tot = 0;
 
-	seq_printf(m, "\tPriority %d, GuC ctx index: %u, PD offset 0x%x\n",
-		client->priority, client->ctx_index, client->proc_desc_offset);
+	seq_printf(m, "\tPriority %d, GuC stage index: %u, PD offset 0x%x\n",
+		client->priority, client->stage_id, client->proc_desc_offset);
 	seq_printf(m, "\tDoorbell id %d, offset: 0x%lx, cookie 0x%x\n",
 		client->doorbell_id, client->doorbell_offset, client->doorbell_cookie);
 	seq_printf(m, "\tWQ size %d, offset: 0x%x, tail %d\n",