Allow selective runtime register synchronization

Allow selective runtime register synchronization

We want to avoid expensive register synchronization IOCTL's on the hot path so
a new kvm_s390_get_registers_partial() is introduced as a compliment to
kvm_arch_get_registers().  The new function is called on the hot path, and
kvm_arch_get_registers() is called when we need the complete runtime register
state.

kvm_arch_put_registers() is updated to only sync the partial runtime set when
we've only dirtied the partial runtime set.  This is to avoid sending bad data
back to KVM if we've only partially synced the runtime register set.

Signed-off-by: Jason J. Herne <jjherne@us.ibm.com>
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Alexander Graf <agraf@suse.de>