kexec: fail image loads if the page tables cannot be built

kexec: fail image loads if the page tables cannot be built

CID 1128566

If an image source page is allocated in kimage_alloc_page() but the
machine_kexec_add_page() fails, the image may appear to load
succesfully but it will not execute.  The relocation will fault
(rebooting the host) when trying to copy the source page, as it is not
mapped.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>