i.MX clock changes for 6.15

- Add missing AXI clock to the i.MX8MP AUDIOMIX in dt-bindings schema.
- Fix DSP and OCRAM_A parent clocks in i.MX8MP AUDIOMIX clock provider.
- Document vendor specific operating-mode property in i.MX8M clock
  provider dt-bindings schema.
- Apply overdrive/nominal constraints based on DT property in i.MX8MP
  clock provider.

clk: imx8mp: inform CCF of maximum frequency of clocks

The IMX8MPCEC datasheet lists maximum frequencies allowed for different
modules. Some of these limits are universal, but some depend on
whether the SoC is operating in nominal or in overdrive mode.

The imx8mp.dtsi currently assumes overdrive mode and configures some
clocks in accordance with this. Boards wishing to make use of nominal
mode will need to override some of the clock rates manually.

As operating the clocks outside of their allowed range can lead to
difficult to debug issues, it makes sense to register the maximum rates
allowed in the driver, so the CCF can take them into account.

Reviewed-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Link: https://lore.kernel.org/r/20250218-imx8m-clk-v4-6-b7697dc2dcd0@pengutronix.de
Signed-off-by: Abel Vesa <abel.vesa@linaro.org>