scsi: target: Create and use macro helpers for per-CPU stats

scsi: target: Create and use macro helpers for per-CPU stats

Create some macros to reduce code duplication for when we handle per-CPU
stats. Convert the existing LUN and auth cases.

Note: This is similar to percpu_counters but they only support s64 since
they are also used for non-stat counters where you need to handle/prevent
rollover more gracefully. Our use is just for stats where the spec
defines u64 use plus we already have some files exporting u64 values so
it's not possible to directly use percpu_counters.

Signed-off-by: Mike Christie <michael.christie@oracle.com>
Reviewed-by: Dmitry Bogdanov <d.bogdanov@yadro.com>
Link: https://patch.msgid.link/20250917221338.14813-3-michael.christie@oracle.com
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>