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/intel_guc_loader.c b/drivers/gpu/drm/i915/intel_guc_loader.c
index 62ebf56..7d92321 100644
--- a/drivers/gpu/drm/i915/intel_guc_loader.c
+++ b/drivers/gpu/drm/i915/intel_guc_loader.c
@@ -151,8 +151,8 @@ static void guc_params_init(struct drm_i915_private *dev_priv)
 	/* If GuC submission is enabled, set up additional parameters here */
 	if (i915.enable_guc_submission) {
 		u32 ads = guc_ggtt_offset(guc->ads_vma) >> PAGE_SHIFT;
-		u32 pgs = guc_ggtt_offset(dev_priv->guc.ctx_pool);
-		u32 ctx_in_16 = GUC_MAX_GPU_CONTEXTS / 16;
+		u32 pgs = guc_ggtt_offset(dev_priv->guc.stage_desc_pool);
+		u32 ctx_in_16 = GUC_MAX_STAGE_DESCRIPTORS / 16;
 
 		params[GUC_CTL_DEBUG] |= ads << GUC_ADS_ADDR_SHIFT;
 		params[GUC_CTL_DEBUG] |= GUC_ADS_ENABLED;