Add Firmware Image Package (FIP) driver ...

The Firmware Image Package (FIP) driver allows for data to be loaded
from a FIP on platform storage. The FVP supports loading bootloader
images from a FIP located in NOR FLASH.

The implemented FVP policy states that bootloader images will be
loaded from a FIP in NOR FLASH if available and fall back to loading
individual images from semi-hosting.

NOTE:
- BL3-3(e.g. UEFI) is loaded into DRAM and needs to be configured
  to run from the BL33_BASE address. This is currently set to
  DRAM_BASE+128MB for the FVP.

Change-Id: I2e4821748e3376b5f9e467cf3ec09509e43579a0

Implement load_image in terms of IO abstraction ...

The modified implementation uses the IO abstraction rather than
making direct semi-hosting calls.  The semi-hosting driver is now
registered for the FVP platform during initialisation of each boot
stage where it is used.  Additionally, the FVP platform includes a
straightforward implementation of 'plat_get_image_source' which
provides a generic means for the 'load_image' function to determine
how to access the image data.

Change-Id: Ia34457b471dbee990c7b3c79de7aee4ceea51aa6