hw/misc/iotkit-sysctl: Handle CPU_WAIT, NMI_ENABLE for SSE-300

hw/misc/iotkit-sysctl: Handle CPU_WAIT, NMI_ENABLE for SSE-300

In the SSE-300 the CPU_WAIT and NMI_ENABLE registers have
moved offsets, so they are now where the SSE-200's WICCTRL
and EWCTRL were. The SSE-300 does not have WICCTLR or EWCTRL
at all, and the old offsets are reserved:

 Offset    SSE-200      SSE-300
-----------------------------------
 0x118     CPUWAIT      reserved
 0x118     NMI_ENABLE   reserved
 0x120     WICCTRL      CPUWAIT
 0x124     EWCTRL       NMI_ENABLE

Handle this reshuffle, and the fact that SSE-300 has only
one CPU and so only one active bit in CPUWAIT.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Tested-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210219144617.4782-15-peter.maydell@linaro.org