Disable automatic dependencies in DKMS package

By default additional dependencies are generated automatically for
packages. This is normally a good thing because it helps ensure
things just work. It doesn't make sense for the DKMS package which
requires minimal dependencies that can be easily listed.

Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: loli10K <ezomori.nozomu@gmail.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #6467
Closes #6835