ARM i.MX1: implement clocks using common clock framework

This also changes the DMA clkdev lookup to use the imx-dma driver name
and "ahb" as connection ID to request the hclk dma clock.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>