anv: Change default PAT entry to WC

i915 mmap_calc_flags() is calculating WC caching for all MTL memory
types.
It will be fixed in the next patch but doing so causes tests to
fail due to incoherency in BOs not allocated with
VK_MEMORY_PROPERTY_HOST_COHERENT_BIT.

So here switching the default/non-coherent BO allocation to a WC
PAT entry.

Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/26099>

src/intel/vulkan/anv_device.c

@@ -4965,5 +4965,5 @@ anv_device_get_pat_entry(struct anv_device *device,
    else if (alloc_flags & (ANV_BO_ALLOC_EXTERNAL | ANV_BO_ALLOC_SCANOUT))
       return &device->info->pat.scanout;
    else
-      return &device->info->pat.writeback;
+      return &device->info->pat.writecombining;
 }