bfd_get_relocated_section_contents allow NULL data buffer
This patch removes the bfd_malloc in default_indirect_link_order and
bfd_simple_get_relocated_section_contents, pushing the allocation down
to bfd_get_relocated_section_contents. The idea is to make use of the
allocation done with sanity checking in bfd_get_full_section_contents,
which is called by bfd_generic_get_relocated_section_contents.
Doing this exposed a bug in bfd_get_full_section_contents. With
relaxation it is possible that an input section rawsize is different
to the section size. In that case we want to use the larger of
rawsize (the on-disk size for input sections) and size.