Add i.MX8QM AHCI "fsl,imx8qm-ahci" compatible strings.

i.MX8QM AHCI SATA doesn't require AHB clock rate to set the vendor
specified TIMER1MS register. ahb clock is not required by i.MX8QM AHCI.

Update the description of clocks in the dt-binding accordingly.
Signed-off-by: Richard Zhu <hongxing.zhu@nxp.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://lore.kernel.org/r/1723428055-27021-2-git-send-email-hongxing.zhu@nxp.comSigned-off-by: Niklas Cassel <cassel@kernel.org>