dmaengine: dw: don't handle interrupt when dmaengine is not used

When dma controller is not used by any user and set off,
we should disble interrupt handler, at least the interrupt
reset part, for some subsystem, e.g. ADSP, may use the
dma in its own logic, here reset the interrupt may make
this subsystem work abnormally.

Signed-off-by: Jie Yang <yang.jie@intel.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>