Often, in traiging core files, one only has a traceback of where a
panic occurred. We have probe* and xpt* routines that live in both the
scsi and ata layers with identical names. To make one or the other
stand out, prefix all the probe and xpt routines in ata with an
'a'. I've left the scsi ones alone since they were there first and are
more numerous. I also rejected using #define to do this as being too
confusing. I chose this method because the CAM name for the probe
device was already 'aprobe'.

Normally, this doesn't matter because file scope protects one from
interfering with the other. However, due to the indirect nature of
CAM's state machine, you don't know if the following traceback is
SCSI or ATA:
	xpt_done
	probedone
	xpt_done_process
	xpt_done_td
	fork_exit

nvme and mmc already have unique names.

MFC: 1 week
Differential revision: https://reviews.freebsd.org/D24825