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
diff --git a/plat/fvp/platform.h b/plat/fvp/platform.h
index 1b0a736..ece882f 100644
--- a/plat/fvp/platform.h
+++ b/plat/fvp/platform.h
@@ -35,6 +35,7 @@
 #include <mmio.h>
 #include <psci.h>
 #include <bl_common.h>
+#include "io_storage.h"
 
 
 /*******************************************************************************
@@ -347,6 +348,11 @@
 extern unsigned int plat_get_aff_count(unsigned int, unsigned long);
 extern unsigned int plat_get_aff_state(unsigned int, unsigned long);
 
+/* Declarations for plat_io_storage.c */
+extern void io_setup(void);
+extern int plat_get_image_source(const char *image_name,
+		io_dev_handle *dev_handle, void **image_spec);
+
 #endif /*__ASSEMBLY__*/
 
 #endif /* __PLATFORM_H__ */