x86: parse Dom0 kernel for PVHv2

x86: parse Dom0 kernel for PVHv2

Introduce a helper to parse the Dom0 kernel.

A new helper is also introduced to libelf, that's used to store the destination
vcpu of the domain. This parameter is needed when loading the kernel on a HVM
domain (PVHv2), since hvm_copy_to_guest_phys requires passing the destination
vcpu.

While there also fix image_base and image_start to be of type "void *", and do
the necessary fixup of related functions.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>