Revert "KVM: PPC: Book3S HV Nested: Stop forwarding all HFUs to L1"

This reverts commit 7c3ded57.

On PowerNV, when a nested guest tries to use a feature prohibited by
HFSCR, the nested hypervisor (L1) should get a H_FAC_UNAVAILABLE trap
so that L1 can emulate the feature. But with the change introduced by
commit 7c3ded57 ("KVM: PPC: Book3S HV Nested: Stop forwarding all HFUs
to L1") the L1 ends up getting a H_EMUL_ASSIST because of which, the L1
ends up injecting a SIGILL when L2 (nested guest) tries to use doorbells.

Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Gautam Menghani <gautam@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://patch.msgid.link/20241109063301.105289-2-gautam@linux.ibm.com