cpu: Introduce CPUClass::parse_features() hook

Adapt the X86CPU implementation to suit the generic hook.
This involves a cleanup of error handling to cope with NULL errp.

Signed-off-by: Andreas Färber <afaerber@suse.de>
target-sparc: Use error_report() for CPU error reporting

Replace non-debug fprintf() with error_report().

Tested-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Signed-off-by: Andreas Färber <afaerber@suse.de>
target-sparc: Implement CPUClass::parse_features() for SPARCCPU

Factor cpu_model parsing out of cpu_sparc_find_by_name() by passing
cpu_sparc_find_by_name() the name portion only and calling
CPUClass::parse_features() from cpu_sparc_register() afterwards.

Tested-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Signed-off-by: Andreas Färber <afaerber@suse.de>
target-sparc: Defer SPARCCPU feature inference to QOM realize

Gets it out of cpu_sparc_register() and aligns with target-arm.

Tested-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Signed-off-by: Andreas Färber <afaerber@suse.de>
cpu: Implement CPUClass::parse_features() for the rest of CPUs

CPUs who do not provide their own implementation of feature parsing
will treat each option as a QOM property and set it to the supplied
value.

Signed-off-by: Andreas Färber <afaerber@suse.de>
cpu: Factor out cpu_generic_init()

All targets using it gain the ability to set -cpu name,key=value,...
options via the default TYPE_CPU CPUClass::parse_features() implementation.

Signed-off-by: Andreas Färber <afaerber@suse.de>