load_image_targphys() gets passed a max size for the file, but doesn't
enforce it at all. Add a check and return -1 (error) if the file is
too big, without loading it.  Fix the bracing style in the function
while we're at it.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Alexander Graf <agraf@suse.de>