genirq/affinity: Rename irq_build_affinity_masks as group_cpus_evenly

Map irq vector into group, which allows to abstract the algorithm for
a generic use case outside of the interrupt core.

Rename irq_build_affinity_masks as group_cpus_evenly, so the API can be
reused for blk-mq to make default queue mapping even though irq vectors
aren't involved.

No functional change, just rename vector as group.

Signed-off-by: Ming Lei <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Reviewed-by: Jens Axboe <[email protected]>                                                                                                                                                                                                    
Link: https://lore.kernel.org/r/[email protected]

Author: Ming Lei