cxl: export internal structs for external Type2 drivers

cxl: export internal structs for external Type2 drivers

In preparation for type2 support, move structs and functions a type2
driver will need to access to into a new shared header file.

Differentiate between public and private data to be preserved by type2
drivers.

Signed-off-by: Alejandro Lucero <alucerop@amd.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Tested-by: Alison Schofield <alison.schofield@intel.com>
Reviewed-by: Gregory Price <gourry@gourry.net>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Link: https://patch.msgid.link/20260306164741.3796372-3-alejandro.lucero-palau@amd.com
Signed-off-by: Dave Jiang <dave.jiang@intel.com>