KVM: PPC: Use arch_get_random_seed_long instead of powernv variant

The powernv_get_random_long() does not work in nested KVM (which is
pseries) and produces a crash when accessing in_be64(rng->regs) in
powernv_get_random_long().

This replaces powernv_get_random_long with the ppc_md machine hook
wrapper.
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Reviewed-by: Fabiano Rosas <farosas@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210805075649.2086567-1-aik@ozlabs.ru

arch/powerpc/kvm/book3s_hv.c

@@ -1165,7 +1165,7 @@ int kvmppc_pseries_do_hcall(struct kvm_vcpu *vcpu)
 		break;
 #endif
 	case H_RANDOM:
-		if (!powernv_get_random_long(&vcpu->arch.regs.gpr[4]))
+		if (!arch_get_random_seed_long(&vcpu->arch.regs.gpr[4]))
 			ret = H_HARDWARE;
 		break;
 	case H_RPT_INVALIDATE: