At the moment kvmppc_mmu_map_page() returns -1 if
mmu_hash_ops.hpte_insert() fails for any reason so the page fault handler
resumes the guest and it faults on the same address again.

This adds distinction to kvmppc_mmu_map_page() to return -EIO if
mmu_hash_ops.hpte_insert() failed for a reason other than full pteg.
At the moment only pSeries_lpar_hpte_insert() returns -2 if
plpar_pte_enter() failed with a code other than H_PTEG_FULL.
Other mmu_hash_ops.hpte_insert() instances can only fail with
-1 "full pteg".

With this change, if PR KVM fails to update HPT, it can signal
the userspace about this instead of returning to guest and having
the very same page fault over and over again.
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>