libaio,io_uring: rename prio_prep() to include cmdprio in the name

libaio,io_uring: rename prio_prep() to include cmdprio in the name

The default priority (which is either 0 or the value set by "prio" and
"prioclass" options, will now be used regardless if prio_prep() is
called or not. This is true for both libaio and io_uring.

The way to think about it is that prio_prep() is only called if
cmdprio_percentage/cmdprio_bssplit is used.

prio_prep() might then override the default priority, if the random
value happens to say that this I/O should use the cmdprio_value,
rather than the default priority.

Rename the prio_prep() functions to highlight that these functions
are now only called if cmdprio is used. (If only option
"prio"/"prioclass" is used, that is handled elsewhere.)

Signed-off-by: Niklas Cassel <niklas.cassel@wdc.com>
Reviewed-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Link: https://lore.kernel.org/r/20211112095428.158300-6-Niklas.Cassel@wdc.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>