target/loongarch: Fix error handling of KVM feature checks

target/loongarch: Fix error handling of KVM feature checks

For some paravirt KVM features, if user forces to enable it however
KVM does not support, qemu should fail to run and exit immediately,
rather than continue to run. Here set error message and return directly
in function kvm_arch_init_vcpu().

Fixes: 6edd2a9bec90 (target/loongarch/kvm: Implement LoongArch PMU extension)
Fixes: 936c3f4d7916 (target/loongarch: Use auto method with LSX feature)
Fixes: 5e360dabedb1 (target/loongarch: Use auto method with LASX feature)
Fixes: 620d9bd0022e (target/loongarch: Add paravirt ipi feature detection)
Signed-off-by: Bibo Mao <maobibo@loongson.cn>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20250320032158.1762751-2-maobibo@loongson.cn>
Signed-off-by: Markus Armbruster <armbru@redhat.com>