mini-os/tpmback: set up callbacks before enumeration

mini-os/tpmback: set up callbacks before enumeration

The open/close callbacks in tpmback cannot be properly initalized in
order to catch the initial enumeration events because init_tpmback
clears the callbacks and then asynchronously starts the enumeration of
existing tpmback devices. Fix this by passing the callbacks to
init_tpmback so they can be installed before enumeration.

This also removes the unused callbacks for suspend and resume.

Signed-off-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>