hw/misc/mps2-scc: Factor out which-board conditionals

hw/misc/mps2-scc: Factor out which-board conditionals

The MPS SCC device has a lot of different flavours for the various
different MPS FPGA images, which look mostly similar but have
differences in how particular registers are handled.  Currently we
deal with this with a lot of open-coded checks on scc_partno(), but
as we add more board types this is getting a bit hard to read.

Factor out the conditions into some functions which we can
give more descriptive names to.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20240206132931.38376-7-peter.maydell@linaro.org