cdx: add cdx controller

cdx: add cdx controller

CDX controller uses MCDI interface as a protocol to
communicate with the RPU firmware and registers the
detected CDX devices on the CDX bus. It also uses
RPMsg as the communication channel with the Firmware.

Signed-off-by: Nipun Gupta <nipun.gupta@amd.com>
Signed-off-by: Puneet Gupta <puneet.gupta@amd.com>
Signed-off-by: Abhijit Gangurde <abhijit.gangurde@amd.com>
Signed-off-by: Nikhil Agarwal <nikhil.agarwal@amd.com>
Reviewed-by: Pieter Jansen van Vuuren <pieter.jansen-van-vuuren@amd.com>
Tested-by: Nikhil Agarwal <nikhil.agarwal@amd.com>
Link: https://lore.kernel.org/r/20230313132636.31850-6-nipun.gupta@amd.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>