The intent of io_init() was to allow platform ports to provide
a data object (io_plat_data_t) to the IO storage framework to
allocate into. The abstraction was incomplete because io_plat_data_t
uses a platform defined constant and the IO storage framework
internally allocates other arrays using platform defined constants.

This change simplifies the implementation by instantiating the
supporting objects in the IO storage framework itself. There is now
no need for the platform to call io_init().

The FVP port has been updated accordingly.

THIS CHANGE REQUIRES ALL PLATFORM PORTS THAT USE THE IO STORAGE
FRAMEWORK TO BE UDPATED.

Change-Id: Ib48ac334de9e538064734334c773f8b43df3a7dc