MAINTAINERS: update the LSM entry

MAINTAINERS: update the LSM entry

Bring the LSM / "SECURITY SUBSYSTEM" entry up to date with the
following changes:

* Remove the "(suggested Cc:)" note on the mailing list.  I don't
really care if the LSM list is on the To: or Cc: line, I just want
folks to include it when appropriate.

* Remove the website link.  The website isn't really maintained in
any meaningful way so we're going to go ahead and remove it so we
lessen the chance of conflicting or confusing information in the
future.

* Add our patchwork link.  I'm not sure this is of much use for
anyone but the maintainer, but there is a provision for including it
here so we might as well include it.

* Add a bug report URI.  I suspect most everyone knows to send mail
to the mailing list if they hit a bug, but let's make it official.

* Add a link to the LSM tree process/management documentation.  While
the doc exists both in the canonical kernel.org location and the
GitHub mirror, provide a link to the mirror as GitHub does a better
job rendering the Markdown.

* Update the source tree's git URI to use https.

* Aside from changes to the LSM code itself, we also would like to be
notified when the LSM call sites are changed so we are adding a
security_XXX(...) regex to try and catch all of the callers.

Signed-off-by: Paul Moore <paul@paul-moore.com>