hw/cxl: Add utility functions decoder interleave ways and target count.

hw/cxl: Add utility functions decoder interleave ways and target count.

As an encoded version of these key configuration parameters is available
in a register, provide functions to extract it again so as to avoid
the need for duplicating the storage.

Whilst here update the _enc() function to include additional values
as defined in the CXL 3.0 specification. Whilst they are not
currently used in the emulation, they may be in future and it is
easier to compare with the specification if all values are covered.

Add a spec reference for cxl_interleave_ways_enc() for consistency
with the target count equivalent (and because it's nice to know where
the magic numbers come from).

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Fan Ni <fan.ni@samsung.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Message-Id: <20230913132523.29780-3-Jonathan.Cameron@huawei.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>