powerpc/powernv: Add platform-specific services for opencapi

Implement a few platform-specific calls which can be used by drivers:

- provide the Transaction Layer capabilities of the host, so that the
  driver can find some common ground and configure the device and host
  appropriately.

- provide the hw interrupt to be used for translation faults raised by
  the NPU

- map/unmap some NPU mmio registers to get the fault context when the
  NPU raises an address translation fault

The rest are wrappers around the previously-introduced opal calls.

Signed-off-by: Frederic Barrat <fbarrat@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>