multimedia/motion - patch to Makefile

[Curtis Villamizar]

I just submitted https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=228102

This has a patch to Makefile adding a WEBCAMD option which allows
multimedia/webcamd to be built without forcing a run time depend on
the long obsolete multimedia/pwcbsd which it then doesn't use.

I left the PWCBSD option in place and unchanged but unless someone has
a sentimental attachment to the PWCBSD option it should probably be
removed.  It does no harm so I left it.

An advantage of this patch, besides avoiding building and installing
the pwcbsd.ko kernel module and in doing so requiring kernel source to
be present, is it avoids a conflict with the multimedia/pwcview port.
pwcview provides a nice simple way to test support for a camera before
using motion to do the real work.

Curtis