LinuxKPI: add dmam_pool_create() support

dmam_pool_create() is a "managed" version of dma_pool_create() which
will cleanup everything left when the device goes away using the
devres framework. For that add an internal cleanup function to be
called from devres release.
This is used by at least one wireless driver.

Sponsored by: The FreeBSD Foundation
MFC after: 10 days
Reviewed by: hselasky
Differential Revision: https://reviews.freebsd.org/D30520