KVM: PPC: Book3S PR: Fix contents of SRR1 when injecting a program exception

vcpu->arch.shadow_srr1 only contains usable values for injecting
a program exception into the guest if we entered the function
kvmppc_handle_exit_pr() with exit_nr == BOOK3S_INTERRUPT_PROGRAM.
In other cases, the shadow_srr1 bits are zero. Since we want to
pass an illegal-instruction program check to the guest, set
"flags" to SRR1_PROGILL for these other cases.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>