anv: Nuke ANV_BO_ALLOC_WRITE_COMBINE

anv: Nuke ANV_BO_ALLOC_WRITE_COMBINE

In i915 if the device has local memory it can only mmap bo with
I915_MMAP_OFFSET_FIXED, so all this set of ANV_BO_ALLOC_WRITE_COMBINE
were useless.

In Xe KMD there is no way to change mmap mode for all GPUs types.

So we can nuke bo->map_wc, ANV_BO_ALLOC_WRITE_COMBINE and related
dead code.

No changes in behavior expected here.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/22483>