intel: Return a bool from intel_aux_map_add_mapping

intel: Return a bool from intel_aux_map_add_mapping

Make intel_aux_map_add_mapping return false if a mapping is attempted
that would conflict with an existing one. If this function doesn't
return false, it will either fail to return or return true.

The Vulkan driver will make use of this feature to opportunistically
enable CCS if a BO's VMA range has not been already mapped.

Reviewed-by: Jianxun Zhang <jianxun.zhang@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25003>