ima: do not copy measurement list to kdump kernel

ima: do not copy measurement list to kdump kernel

Kdump kernel doesn't need IMA to do integrity measurement.
Hence the measurement list in 1st kernel doesn't need to be copied to
kdump kernel.

Here skip allocating buffer for measurement list copying if loading
kdump kernel. Then there won't be the later handling related to
ima_kexec_buffer.

Signed-off-by: Steven Chen <chenste@linux.microsoft.com>
Tested-by: Baoquan He <bhe@redhat.com>
Acked-by: Baoquan He <bhe@redhat.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>