MIPS: jz4740: Acquire and enable DMA controller clock

Previously, it was assumed that the DMA controller clock is not gated
when the kernel starts running. While that is the power-on state, it is
safer to not rely on that.

Signed-off-by: Maarten ter Huurne <maarten@treewalker.org>
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Acked-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>