refactor(measured boot): move image measurement to generic layer

Right now, the assumption is that the platform post-load hook takes
care of measuring the image that just got loaded. This is how it's
implemented on FVP.

This patch moves the measurement into the generic code
instead. load_auth_image() now calls plat_mboot_measure_image(),
which is a new platform interface introduced in this patch to measure
an image. This is called just after authenticating the image.

Implement plat_mboot_measure_image() for the Arm FVP platform. The code
is copied straight from the post-load hook.

As a result, the FVP specific implementation of
arm_bl2_plat_handle_post_image_load() is no longer needed. We can go
back to using the Arm generic implementation of it.

Change-Id: I7b4b8d28941a865e10af9d0eadaf2e4850942090
Signed-off-by: Sandrine Bailleux <sandrine.bailleux@arm.com>
Signed-off-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>
diff --git a/include/plat/common/platform.h b/include/plat/common/platform.h
index 5fc21a5..bbf8ee80 100644
--- a/include/plat/common/platform.h
+++ b/include/plat/common/platform.h
@@ -213,6 +213,7 @@
 
 void bl2_plat_mboot_init(void);
 void bl2_plat_mboot_finish(void);
+int plat_mboot_measure_image(unsigned int image_id);
 #else
 static inline void bl2_plat_mboot_init(void)
 {
@@ -220,6 +221,10 @@
 static inline void bl2_plat_mboot_finish(void)
 {
 }
+static inline int plat_mboot_measure_image(unsigned int image_id __unused)
+{
+	return 0;
+}
 #endif /* MEASURED_BOOT */
 
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