intel/device: bdw_gt1 actually has 6 eus per subslice

Found by inspection, I'm not aware of any bugs caused by this typo.

According to Lionel, it seems we only use this to generate masks
of available EUs for perfromance queries, and it's only used when we
can't query the fused parts of the GPU through DRM_IOCTL_I915_QUERY.
So this patch should help for the corner case where the Kernel is too
old to support the query ioctl.

v2: improve commit message, cc stable (Lionel).

Cc: mesa-stable@lists.freedesktop.org
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4006>
(cherry picked from commit aa78801f0a)

.pick_status.json

@@ -400,7 +400,7 @@
         "description": "intel/device: bdw_gt1 actually has 6 eus per subslice",
         "nominated": true,
         "nomination_type": 0,
-        "resolution": 0,
+        "resolution": 1,
         "master_sha": null,
         "because_sha": null
     },

src/intel/dev/gen_device_info.c

@@ -434,7 +434,7 @@ static const struct gen_device_info gen_device_info_bdw_gt1 = {
    .is_broadwell = true,
    .num_slices = 1,
    .num_subslices = { 2, },
-   .num_eu_per_subslice = 8,
+   .num_eu_per_subslice = 6,
    .l3_banks = 2,
    .max_cs_threads = 42,
    .urb = {