livepatch: Add limit of 2MB to payload .bss sections.

livepatch: Add limit of 2MB to payload .bss sections.

The initial patch: 11ff40fa7bb5fdcc69a58d0fec49c904ffca4793
"xen/xsplice: Hypervisor implementation of XEN_XSPLICE_op" caps the
size of the binary at 2MB. We follow that in capping the size
of the .BSSes to be at maximum 2MB.

We also bubble up the payload limit and this one in one #define
called LIVEPATCH_MAX_SIZE to make it easier to find these
arbitrary limits.

Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Ross Lagerwall <ross.lagerwall@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>