IB/ehca: Deprecate driver, move to staging, schedule deletion

The ehca driver is only supported on IBM machines with a custom EBus.
As they have opted to build their newer machines using more industry
standard technology and haven't really been pushing EBus capable
machines for a while, this driver can now safely be moved to the
staging area and scheduled for eventual removal.  This plan was brought
to IBM's attention and received their sign-off.

Cc: alexs@linux.vnet.ibm.com
Cc: hnguyen@de.ibm.com
Cc: raisch@de.ibm.com
Cc: stefan.roscher@de.ibm.com
Signed-off-by: Doug Ledford <dledford@redhat.com>