KVM: PPC: Book3S: Add ONE_REG register names that were missed

Commit 3b783474 ("KVM: PPC: Book3S HV: Reserve POWER8 space in get/set_one_reg") added definitions for several KVM_REG_PPC_* symbols
but missed adding some to api.txt.  This adds them.
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>

Documentation/virtual/kvm/api.txt

@@ -1794,6 +1794,11 @@ registers, find a list below:
   PPC   | KVM_REG_PPC_MMCR0     | 64
   PPC   | KVM_REG_PPC_MMCR1     | 64
   PPC   | KVM_REG_PPC_MMCRA     | 64
+  PPC   | KVM_REG_PPC_MMCR2     | 64
+  PPC   | KVM_REG_PPC_MMCRS     | 64
+  PPC   | KVM_REG_PPC_SIAR      | 64
+  PPC   | KVM_REG_PPC_SDAR      | 64
+  PPC   | KVM_REG_PPC_SIER      | 64
   PPC   | KVM_REG_PPC_PMC1      | 32
   PPC   | KVM_REG_PPC_PMC2      | 32
   PPC   | KVM_REG_PPC_PMC3      | 32