dt-bindings: mfd: fsl,imx8qxp-csr: Remove binding documentation

dt-bindings: mfd: fsl,imx8qxp-csr: Remove binding documentation

commit b0a5cde57cf1 ("dt-bindings: mfd: Explain lack of child dependency
in simple-mfd") pointed out that it's a mistake for a child device of
a simple MFD device to depend on the simple MFD device's clock resources.
fsl,imx8qxp-csr.yaml happens to make that mistake.  To fix that, remove
fsl,imx8qxp-csr.yaml and use "simple-pm-bus" and "syscon" as the CSR node's
compatible strings in the examples of fsl,imx8qxp-pixel-link-msi-bus.yaml
to replace the wrong compatible strings which include "simple-mfd" and
"fsl,imx8qxp-mipi-lvds-csr".  Since fsl,imx8qxp-pixel-link-msi-bus.yaml
as the last user of the CSR compatible strings no longer uses them, it's
safe to remove the fsl,imx8qxp-csr.yaml binding documentation.

Fixes: 9b2c55b5403f ("dt-bindings: mfd: Add i.MX8qm/qxp Control and Status Registers module binding")
Fixes: c08645ea215c ("dt-bindings: bus: Add Freescale i.MX8qxp pixel link MSI bus binding")
Signed-off-by: Liu Ying <victor.liu@nxp.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://lore.kernel.org/r/20250620022537.3072877-1-victor.liu@nxp.com
Signed-off-by: Lee Jones <lee@kernel.org>