s390x/kvm: Reworked/fixed handling of cc3 in kvm_handle_css_inst()

s390x/kvm: Reworked/fixed handling of cc3 in kvm_handle_css_inst()

Consolidated the setting of the condition code in kvm_handle_css_inst().
For the (unhandled) instructions EQBS and SQBS, we have to return
an operation exception instead of cc3. Also removed the is_ioinst()
function to avoid decoding the opcode twice.

Signed-off-by: Thomas Huth <thuth@linux.vnet.ibm.com>
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>