SOLARIS: Free vcache mappings on shutdown

SOLARIS: Free vcache mappings on shutdown

Right before shutdown, go through all of our vcaches and flush them,
freeing any pages associated with the vcaches. If we don't do this,
pages associated with our vcaches may still be around after we
shutdown and the module is unloaded, causing a panic when the kernel
tries to deference the page's vnode.

Abstract out afs_freevfs() following the gafs_foo/afs_foo convention
from the vnode ops, since we're calling this in two different places.

Reviewed-on: http://gerrit.openafs.org/3472
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit 592a33a4787db88993a7bf9d8f5ad8c11a576b56)

Change-Id: I809d10d2eceb7d0db92b3d149b13de0dc9221958
Reviewed-on: http://gerrit.openafs.org/4194
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: BuildBot <buildbot@rampaginggeek.com>