Pass a full set of flags to drivers' per-operation 'prep' routines.
Currently the only flag passed is DMA_PREP_INTERRUPT.  The expectation is
that arch-specific async_tx_find_channel() implementations can exploit this
capability to find the best channel for an operation.
Signed-off-by: NDan Williams <dan.j.williams@intel.com>
Acked-by: NShannon Nelson <shannon.nelson@intel.com>
Reviewed-by: NHaavard Skinnemoen <hskinnemoen@atmel.com>