LinuxKPI: tasklet add (*callback) support

LinuxKPI: tasklet add (*callback) support

In addition to (*func) tasklet also seems to have a (*callback) with
a different argument.  Add support for this and add tasklet_setup()
as well for support in more drivers.

The from_tasklet() definition is duplicated in the tree; hide it there
under #ifndef to avoid a re-definition.  People should generally add
LinuxKPI bits to linuxkpi rather than private files if they also rely
on other LinuxKPI bits.

X-MFC:		DO NOT MFC, space allocated by drivers not us.
Reviewed by:	emaste
Differential Revision: https://reviews.freebsd.org/D37216