dynrelas support, obsoleting link-vmlinux-syms

This adds dynamic linking support for the patch modules.  It is the
first step toward supporting patching module code and relocatable
kernels.

Rela entries that reference non-included local and non-exported global
symbols are converted to "dynrelas".  These dynrelas are relocations
that are done by the core module, not the kernel module linker.  This
allows the core module to apply offsets to the base addresses found
in the base vmlinux or module.

Signed-off-by: Seth Jennings <sjenning@redhat.com>

Conflicts:
	kpatch-build/kpatch-build
fix review comments

Signed-off-by: Seth Jennings <sjenning@redhat.com>
remove redundant rela buffer rebuild

We rebuild the rela section data buffer in kpatch_create_rela_section()
just to rebuild it again later in kpatch_rebuild_rela_section_data()
before writing the output ELF file.

This commit removes the redundant rebuild while retaining the update
for the section header data.

Signed-off-by: Seth Jennings <sjenning@redhat.com>
add teardown/free functions for kpatch_elf data structures

Because create-diff-object is a one-shot program (not a long lived
process) we haven't really bothered with cleaning up and freeing any
allocated memory.  However, freeing data when it passes out of the
logical scope does have debugging benefits.

This commit adds two new functions for tearing down and freeing the
primary struct kpatch_elf data structures.  The idea is the if a stale
pointer still references the old data structure that has passed out of
the logical scope, an issue will be more immediately apparent (i.e. NULL
references).

Signed-off-by: Seth Jennings <sjenning@redhat.com>