cxl: Remove support for "Processing accelerators" class

The cxl driver currently declares in its table of supported PCI
devices the class "Processing accelerators". Therefore it may be
called to probe for opencapi devices, which generates errors, as the
config space of a cxl device is not compatible with opencapi.

So remove support for the generic class, as we now have (at least) two
drivers for devices of the same class. Most cxl devices are FPGAs with
a PSL which will show a known device ID of 0x477. Other devices are
really supported by the cxlflash driver and are already listed in the
table. So removing the class is expected to go unnoticed.

Signed-off-by: Frederic Barrat <fbarrat@linux.vnet.ibm.com>
Acked-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>