arm64: dts: imx8mp: correct sdma1 clk and compatible name

arm64: dts: imx8mp: correct sdma1 clk and compatible name

Correct sdma1 compatible name and clock setting in dts, because in the future
'fsl,imx8mp-sdma' is used for sdma2/3 which could be off/on runtime. sdma1 is
kept on always like legacy chips like i.mx8mq/i.mx7d/i.mx6 etc.
Besides, correct sdma1 clock setting since it's 1:2 clock ratio instead of
1:1, otherwise, sdma1 will not work.

Signed-off-by: Robin Gong <yibin.gong@nxp.com>
Reviewed-by: Anson Huang <Anson.Huang@nxp.com>