capi: Enable capi mode for PHB4

Enable the Coherently attached processor interface. The PHB is used as
a CAPI interface.
CAPI Adapters can be connected to either PEC0 or PEC2. Single port
CAPI adapter can be connected to either PEC0 or PEC2, but Dual-Port
Adapter can be only connected to PEC2
   CAPP0 attached to PHB0(PEC0 - single port)
   CAPP1 attached to PHB3(PEC2 - single or dual port)
As we did for PHB3, a new specific file 'phb4-capp.h' is created to
contain the CAPP register definitions.

Signed-off-by: Christophe Lombard <clombard@linux.vnet.ibm.com>
Reviewed-by: Frederic Barrat <fbarrat@linux.vnet.ibm.com>
Signed-off-by: Stewart Smith <stewart@linux.vnet.ibm.com>