xsplice: Add helper elf routines

xsplice: Add helper elf routines

Add Elf routines and data structures in preparation for loading an
xSplice payload.

We make an assumption that the max number of sections an ELF payload
can have is 64. We can in future make this be dependent on the
names of the sections and verifying against a list, but for right now
this suffices.

Also we a whole lot of checks to make sure that the ELF payload
file is not corrupted nor that the offsets point past the file.

For most of the checks we print an message if the hypervisor is built
with debug enabled.

Signed-off-by: Ross Lagerwall <ross.lagerwall@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Release-acked-by: Wei Liu <wei.liu2@citrix.com>