kldload: Bring functionality in line with manual page

Honor -q parameter and do not display any warning messages when -q is
specified.

Approved by: dfr
MFC after: 2 weeks
Sponsored by: Resulta, s.r.o.
Differential Revision: https://reviews.freebsd.org/D35511

(cherry picked from commit ad0a7ea65084e997f21fdb4724120e850b20659b)