emulators/open-vm-{tools,kmod}: split the package

Split the package to build the kmods separatly! Building separately has
multiple benefits:

1. it allows user to rebuild when they upgrade their kernel without rebuilding all of the tools which can take a long time.
2. it allows us to provide the modules in the new kmods package repository
3. it installs the kmods the in the same place as the regular kmods: /boot/modules

It means we can probably get rid of the rc script in favor if letting
users use kld_list mecanism but I will let this decision to the
maintainer based on what it probably best for users.

Approved by: garga (maintainer)
Reviewed by: garga (maintainer)
Differential Revision: https://reviews.freebsd.org/D48059