bl_common: add image_size()
Ryan Harkin authored
Fixes ARM-software/tf-issues#42

Some callers of load_image() may need to get the size of the image
before/after loading it.

Change-Id: I8dc067b69fc711433651a560ba5a8c3519445857
Signed-off-by: default avatarRyan Harkin <ryan.harkin@linaro.org>
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