mlx.4: Improve specificity for apropos + hw notes

+ There are decades of SCSIs, these are Ultra-SCSI
+ Remove generalizations from the end of HARDWARE
+ Tag SPDX

MFC after: 3 days
Reviewed by: mhorne
Approved by: mhorne (mentor)
Differential Revision: https://reviews.freebsd.org/D50545

(cherry picked from commit e3307d05311e8c042e7e7ea2157fc51f50297369)