net: ethernet: ti: davinci_cpdma: fix fixed prio cpdma ctlr configuration

The dma ctlr is reseted to 0 while cpdma soft reset, thus cpdma ctlr
cannot be configured after cpdma is stopped. So restoring content
of cpdma ctlr while off/on procedure is needed. The cpdma ctlr off/on
procedure is present while interface down/up and while changing number
of channels with ethtool. In order to not restore content in many
places, move it to cpdma_ctlr_start().

Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>