anv: allocate tile sized temporary copy instead of whole size

This fixes dEQP-VK.image.host_image_copy.* tests that require temp_copy
on 32bit builds.

Closes: https://gitlab.freedesktop.org/mesa/mesa/-/work_items/15409
Signed-off-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/41533>