drm/xe: refactor xe_mmio_probe_tiles to support MMIO extension

In future ASICs, there will be an additional MMIO extension space
for all tiles altogether, residing on top of MMIO address space.

Signed-off-by: Koby Elbaz <kelbaz@habana.ai>
Reviewed-by: Ofir Bitton <obitton@habana.ai>
Reviewed-by: Moti Haimovski <mhaimovski@habana.ai>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>