shix: Catch CPU initialization errors

Print an error message as done for the r2d machine and exit.

Signed-off-by: Andreas Färber <afaerber@suse.de>
sh7750: Change cpu field type to SuperHCPU

This brings us a step closer to QOM'ified SH7750 SoC and
fixes b350ab75 (target-sh4: Move PVR/PRR/CVR into SuperHCPUClass)
assuming SuperHCPU type for SUPERH_CPU_GET_CLASS().

Fix Coding Style issues while at it (indentation, braces).

Reported-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Andreas Färber <afaerber@suse.de>