Refactor CTL datamove KPI.

• Make frontends call unified CTL core method ctl_datamove_done()

to report move completion. It allows to reduce code duplication
in differerent backends by accounting DMA time in common code.

• Add to ctl_datamove_done() and be_move_done() callback samethr

argument, reporting whether the callback is called in the same
context as ctl_datamove(). It allows for some cases like iSCSI
write with immediate data or camsim frontend write save one context
switch, since we know that the context is sleepable.

• Remove data_move_done() methods from struct ctl_backend_driver,

unused since forever.

MFC after: 1 month