Revert "cxl: Add support for using the kernel API with a real PHB"

Remove abandonned capi support for the Mellanox CX4.

This reverts commit 317f5ef1.

Signed-off-by: Alastair D'Silva <alastair@d-silva.org>
Acked-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>