dmaengine: sirf: move driver init from module_init to subsys_initcall

if we initilize dma driver by module_init, there are still many devices
which will be initilized earlier than dma. these devices will fail to
get dma channel.
this moves dmaengine earlier than device_initcall and make dma available
for all devices.

Reported-by: Renwei Wu <Renwei.Wu@csr.com>
Signed-off-by: Barry Song <Baohua.Song@csr.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>