ppc: Add POWER8 IAMR register

ppc: Add POWER8 IAMR register

With appropriate AMR-like masks. Not actually used by the translation
logic at that point

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
[clg: changed spr_register_hv(SPR_IAMR) to spr_register_kvm_hv(SPR_IAMR)
      changed gen_spr_amr() prototype ]
Signed-off-by: Cédric Le Goater <clg@fr.ibm.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>