ppc: Fix writing to AMR/UAMOR

ppc: Fix writing to AMR/UAMOR

The masks weren't chosen nor applied properly. The architecture specifies
that writes to AMR are masked by UAMOR for PR=1, otherwise AMOR for HV=0.

The writes to UAMOR are masked by AMOR for HV=0

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
[clg: moved gen_spr_amr() prototype change to next patch ]
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>