drm/i915: sseu: Convert subslice count fields to subslice mask

In an upcoming patch we'll need the actual mask of subslices in addition
to their count, so convert the subslice_per_slice field to a mask.
Also we can easily calculate subslice_total from the other fields, so
instead of storing a cached version of this, add a helper to calculate
it.

v2:
- Use hweight8() on u8 typed vars instead of hweight32(). (Ben)

Reviewed-by: Robert Bragg <robert@sixbynine.org> (v1)
Reviewed-by: Ben Widawsky <benjamin.widawsky@intel.com> (v1)
Tested-by: Ben Widawsky <benjamin.widawsky@intel.com> (v1)
Signed-off-by: Imre Deak <imre.deak@intel.com>
diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index 5e22105..02c34d6 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -288,7 +288,7 @@
 		value = i915_cmd_parser_get_version(dev_priv);
 		break;
 	case I915_PARAM_SUBSLICE_TOTAL:
-		value = INTEL_INFO(dev_priv)->sseu.subslice_total;
+		value = sseu_subslice_total(&INTEL_INFO(dev_priv)->sseu);
 		if (!value)
 			return -ENODEV;
 		break;