cpu: make cpu_generic_init() abort QEMU on error

cpu: make cpu_generic_init() abort QEMU on error

Almost every user of cpu_generic_init() checks for
returned NULL and then reports failure in a custom way
and aborts process.
Some users assume that call can't fail and don't check
for failure, though they should have checked for it.

In either cases cpu_generic_init() failure is fatal,
so instead of checking for failure and reporting
it various ways, make cpu_generic_init() report
errors in consistent way and terminate QEMU on failure.

Signed-off-by: Igor Mammedov <[email protected]>
Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
Message-Id: <1505318697[email protected]>
Signed-off-by: Eduardo Habkost <[email protected]>