target/arm/kvm: scratch vcpu: Preserve input kvm_vcpu_init features

target/arm/kvm: scratch vcpu: Preserve input kvm_vcpu_init features

kvm_arm_create_scratch_host_vcpu() takes a struct kvm_vcpu_init
parameter. Rather than just using it as an output parameter to
pass back the preferred target, use it also as an input parameter,
allowing a caller to pass a selected target if they wish and to
also pass cpu features. If the caller doesn't want to select a
target they can pass -1 for the target which indicates they want
to use the preferred target and have it passed back like before.

Signed-off-by: Andrew Jones <drjones@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Tested-by: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>
Reviewed-by: Beata Michalska <beata.michalska@linaro.org>
Message-id: 20191031142734.8590-8-drjones@redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>