hw/cxl: Fix and use same calculation for HDM decoder block size everywhere

hw/cxl: Fix and use same calculation for HDM decoder block size everywhere

In order to avoid having the size of the per HDM decoder register block
repeated in lots of places, create the register definitions for HDM
decoder 1 and use the offset between the first registers in HDM decoder 0 and
HDM decoder 1 to establish the offset.

Calculate in each function as this is more obvious and leads to shorter
line lengths than a single #define which would need a long name
to be specific enough.

Note that the code currently only supports one decoder, so the bugs this
fixes don't actually affect anything.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Fan Ni <fan.ni@samsung.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20230913132523.29780-4-Jonathan.Cameron@huawei.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>